Get to green build.

* Add support to move the fab between positions.

* Motion demo for the FAB works between center and end floating.

* Add a Material curve to the offset animation.

* Move the fab position into an object

* Updates to docs

* Updates to docs

* Fix a lint on the bottom sheet type

* Add a ScaffoldGeometry class

* Improve the documentation

* Improve the documentation

* Add a fab motion animator

* Add position and scale animations

* FAB entrance and motion animations work

* Get started on FAB motion

* Make fab animation work properly.

* Change the fab animator to be stored in the state of the scaffold.

* Add a layout test

* Fix spacing being off

* Fix the entrance/exit animation test.

* Add a textDirection to the layout delegate.

* Fix const constructor lint checks

* Add toStrings for the fab positioner/animator

* Add a toString for CurveTween

* Change the fab motion demo icon to a simple add icon.

* Add tests and a custom fab positioner to the demo.

* Do not start the fab's motion animation when the fab is null.

* Adjust the code to pass the new tests.

* Rename for in response to Hans' comment.

* Revert the tabs fab demo

* Use timeDilation, and clean up the animation code a little.

* Clean up the prelayout geometry docs and ctr order

* Cleanup fab transition widget code

* Clean up comments on Scaffold, add cross-references between the two geometries

* Explain the fab motion animation scheduling better

* Add a const to the fab motion demo

* Make the fab animation never jank by keeping track of where to move the fab to in the future.

* Add a default fab positioner constant

* Add space after comma in the demo

* Add boilerplate dartdoc to all const constructors

* Comment improvement

* Rename 'fabSize' to 'floatingActionButtonSize'

* Rename 'fabSize' to 'floatingActionButtonSize'

* Rename 'fabSize' to 'floatingActionButtonSize'

* Clean up the prelayout geometry object's dartdoc

* Clean up the prelayout geometry object's dartdoc

* Remove extraneous comment

* Change possessive uses of Scaffold's to use dartdoc-compatible [Scaffold]'s

* Rename the horizontalFabPadding to an expansion

* Clean up controller cleanup and setState usage

* Animate instead of lerp

* Make the fab position animation use offsets instead of animations

* Streamline the fab motion demo

* Set up the animator to start from a reasonable place when interrupting animations.

* Doc cleanup on the new animation interruption

* Expand some uses of fab and clean up constants

* Expand remaining public uses of fab to floating action button

* Expand remaining public uses of fab to floating action button

* Expand on the documentation for the fab positioner and animator

* Refactor animations to broadcast the position properly.

* Add the ability to turn on and off the fab to the motion demo.

* Remove unused code

* Change the fab animator to animate even when the fab is exitting.

* Remove extra positioner.

* Apps -> Applications in docs

* Explain the scale animation.

* Name the child parameter in the animated builder

* RTL before LTR

* Wrap the AppBar in the example code

* const the fab motion demo name

* Start a test against animation jumps

* Test for jumps in the fab motion animation

* Dont initialize values to null

* Use constants, fix spacing from some of Hans' comments

* Clarify the relationship between fab positioners and prelayout geometries

* Explain the fab animmator a bit better

* Explain the animation progress in the fab animation

* Explain the animation restart better

* Explain the animation restart better

* Explain the prelayout geometry better

* Explain that height is a vertical distance.

* Explain the horizontal fab padding

* Update the scaffold size description to explain what happens when a wild keyboard appears

* Remove print statements

* Update the scaffold geometry with information about it being available at paint time.

* In one step of a transition

* Explain how the top-start fab positioner works

* Explain how the top-start fab positioner works

* Refactor the scaffold layout to just pass a padding instead of a bottom, top, start and end.

* Refactor the scaffold layout to just pass a padding instead of a bottom, top, start and end.

* Action buttons with with custom positioners.

* Add a rotation animation example.

* Use a swap animation to show swapping between two different animations.

* Use a swap animation to show swapping between two different animations.

* Add an example for the size animations.

* 2018 copyright

* Extra empty line

* Return new Scaffold

* Extra blank line fix

* All its contents have been laid out

* Position the fab

* Explain what the scaffold geometry is for.

* Move asserts to different lines

* The scaffoldsize will not

* Initial rename of FabPositioners to FloatingActionButtonLocation

* Rename comments in example to refer to location instead of positioner.

* Rename fabpositioner to location in tests and in the scaffold field

* Finish removing references to positioner in scaffold code.

* Split the fab location and animation out into a separate file.

* Make things more private

* Import foundation instead of meta

* Const curve instead of final.

* Do not encode the server port in the test file

* revert formatting

* add back ignore

* add a default value to serverPort

* address comments

- picks up dart change to introduce multi root file system for use in
google3 builds

* Upgrade packages to pull in newest petitparser with Dart 2 fixes.

* Don't allow Dart 2 failures.

* Address new lints discovered by updated analyzer.

* iupdate engine version to 141176b9004d7b01325629fd45b2ef61b0d00251

* update engine version to f192c59d76c0afe63f2290c3ed76061f00c77cc7
This rolls dart to version 0175f24b2549732d0010708988fd328440c3f956

* Move dart 2 tests back to optional section to allow debugging of a new
regression in the petitParser package.

* Update

Actual text: "Tab 2 of $3"
Expected text: "Tab 2 of 3"

* Use theme for default icon color

Replaces hard-coded black.

* Better icon defaults for dark/light modes

* Add default case to silence warning

This changes the packaging tool to only set the remote URL instead of recreating the remote.

Recreating it was removing some metadata that identified the repo as having been cloned from the "real" repo, so flutter --version would report an unknown channel and source. This just sets the URL so that it looks like it came from GitHub.

I also fixed some incorrect comments, and made unzip work on platforms other than Windows (even though we don't really need it there yet).

Fixes #15518

* replace child parameter with builder on showDialog

* change builder parameter to WidgetBuilder

* mark child as deprecated and expand documentation to cover this and how builder should be used

* tidy comments and address some feedback

* phrasing

* move space to prev line and add //ignore comments for deprecated member use

* address comments and fix it's its

* update code samples

* adds semicolon to code snippets

* change ThemeData.primaryColor to PrimarySwatch instead of PrimarySwatch[500]

* fix mismatched color in stock test case

This engine has libtxt enabled by default

This change makes the discrete slider show the value indicator for a minimum amount of time for any interaction (tap, drag).

During the review, we determined that it would be good for the value indicator to stretch when the text scale was smaller, and the shrink when it was larger, to keep the value visible over the finger at small sizes, and closer to the finger at large sizes. This implements that change.

Avoids a null pointer exception if dispose() is called on an
already-disposed InkDecoration.

This fixes https://github.com/flutter/flutter/issues/15458.

* Use a set to remove duplicate channel names

* Add test for git command

* Roll engine to b6df7a637498ca9beda1fa9cd7210e3202ea599f.

Changes since last roll:
```
b6df7a637 Roll dart to 290c576264faa096a0b3206c71b2435309d9f904. (#4771)
a6764dbd5 Add sources for Fuchsia target. (#4763)
2d5900615 [fuchsia] Remove unused header file. (#4769)
9717063b7 Revert "Roll dart to c080951d45e79cd25df98036c4be835b284a269c. (#4767)" (#4768)
9a9814312 Roll dart to c080951d45e79cd25df98036c4be835b284a269c. (#4767)
e74e8b35c [async] Update includes of async headers to new path (#4760)
e2c4b2760 Use Dart 2 camel case constants in the engine Dart libraries (#4766)
9c1e48434 Updates for Fuchsia roll. (#4765)
14c940e27 Switch from fxl::Mutex to std::mutex (#4764)
debf82c0b Roll Garnet (#4759)
5bffdefbb Use weak pointers to the accesibility bridge from objects vended to the UIKit accessibility framework. (#4761)
```

* Silence broken test

* Mark test as flaky instead

Plus run_machine_concurrent_hot_reload which isn't all green, but is
green since the fix was pushed.

* Update the following packages
- dart-petitparser to 1.7.5
- dart-xml to 3.0.3
- image to 1.1.30
These updates fix some of the strong mode errors we were encountering
while running flutter tests.