Includes:
* Provide asset lookup key on ios (flutter/engine#4817)
* Load kernel files from the script URI in the isolate create callback (flutter/engine#4828)
* Remove some unneeded profiling flags (flutter/engine#4827)
* Remove the canvas save/restore calls in Paragraph::Paint (flutter/engine#4822)

This caused a test failure in the integration_ui_ios devicelab test.

```
stdout: [   +3 ms] 00:02 [32m+0[0m: end-to-end test Ensure keyboard dismissal resizes the view to original size[0m
stdout: [+8129 ms] 00:11 [32m+0[0m[31m -1[0m: end-to-end test Ensure keyboard dismissal resizes the view to original size [1m[31m[E][0m[0m
stdout: [   +5 ms]   DriverError: Failed to fulfill Tap: Flutter application not responding
stdout: [        ]   Original error: TimeoutException after 0:00:07.500000: Future not completed
stdout: [        ]   Original stack trace:
stdout: [        ]   #0      FlutterDriver._sendCommand (package:flutter_driver/src/driver/driver.dart:324:18)
stdout: [        ]
stdout: [        ]   #1      FlutterDriver.tap (package:flutter_driver/src/driver/driver.dart:368:11)
stdout: [        ]
stdout: [        ]   #2      main.. (file:///[... snip ...]/flutter/dev/integration_tests/ui/test_driver/keyboard_resize_test.dart:34:20)
```

This reverts commit 067be92a.

This reverts commit a7e62258 as there are failing tests.

* Move mockito to 3.0.0-alpha.

This is needed so it matches mockito version used internally.

* Pick up +2 for the fixes

* Fix whenReturn in fuchsia_remote_debug_protocol

* more thenReturn becomes thenAnswer

* more thenReturn becomes thenAnswer

* more thenReturn becomes thenAnswer

Roll engine to version dd6f46c485192f4506035088c9065b9f5dbba9ab

* Address post-submit comments

* Added dispose protection for the animation controllers.

* android templates should add density and screenLayout to config changes

* update the rest of the manifests

* Remove tear-off mocking in refresh_test

* Comments

* Analyzer fix

* Final final final final mushroom mushroom!

* Fix for Dart 1 AND Dart 2 semantics; anonymous closure over tear-off

* Final final

* CONTRIBUTING.md: updates for Dart 2; move parts to flutter/engine

* address comments

* Add more doc linking the material and cupertino refresh controls

* review

* Re-enable usage of TransformLayers with text in RenderListWheelViewport

* add test

* linter fix

Adds a package that will support connecting to and debugging devices with multiple instances of the Dart VM, and operate on multiple Isolates and Flutter Views.

Currently supports connecting to all existing Dart VMs and extracting information about all Flutter Views running across each VM.

This is not a grand refactor yet, it's just cleaning up what we have
already, so that people who keep using this API (e.g. dialogs) have
something coherent to deal with.

The major changes are that Navigator and NavigatorState have the same
API now, that most of the examples use `<void>` instead of `<Null>`,
that the navigator observer can see replaces, and that the `settings`
is moved from ModalRoute to Route. I also cleaned up some of the API
documentation.

* use HttpOverrides and dart:io HttpClient in flutter

* add missing package:http dependency

* update flutter packages and remove comment about createHttpClient from flutter_test

* move byte loading logic to common class, move string parsing logic to base class

* addAll doesn't work for a Uint8List

* use bytes.setRange

* undo addition to hello_world

* add newline to end of binding.dart

* and a newline for hello world

* refactor to function and add tests

* address comments on unknown length case

* alignment

* sort alaphabetically

* rename convertResponse to consolidateClientHttpClientResponseBytes.  Add header

* fix alignment in test

This updates the visual look of the Chip class, so that it scales properly in the face of text scale (and label widget size) changes, and bases its height off of the label widget's height, constraining the other widgets it contains to be the same height.

To do this properly, I had to implement a custom render object that will measure the height of the label, so the guts of this class are basically rewritten.

In addition, to allow the circle avatar to increase in size when the chip does, I added minRadius and maxRadius arguments to it, and I updated its color handling to use the light/dark primary colors of the theme in a smart way instead of just using black and white.

Updated and added tests.

* Gallery scaffolding

* Started RenderSliver

* demo and initial hookup

* Cleaned up demo more and scaffolding basic sliver->widget communication structure.

* works

* states and default indicator building works

* start adding docs

* added an alignment setting optimized the sliver relayout mechanism

* tested a default bottom aligned sized indicator

* Added a bunch of tests

* more fixes and more tests

* Finished the tests

* Add docs

* Add more doc diffing wrt material pull to refresh

* Mention nav bar synergy

* add more asserts

* review 1

* Fix mockito 2 / dart 2 / strong typed tests

* review

* Remove the vscode config

* review

* Add more docs and examples for implementers of RenderSliver

* add more typical scenarios to describe scrollOffset

* review

* tweak a word

Also adds test for interpolating gradient stops.