All artifacts for iOS are universal.

Scrollable sometimes pushes frames forever

Update engine.version

Fix _LazyWidgetProvider indexing, move Ali Connors

We were setting a negative velocity tolerance, which never triggered because we
assume tolerances are positive numbers. Now we use a positive tolerance and
assert to catch this case in the future.

Fixes #2765

Allow customizing of Switch thumbs

Fixes #2621

Flexible AppBar with a TabBar

Improve error message when ChildView lacks a MediaQuery

refactor; fix apk warning

add support for a FLUTTER_DEV env var in the flutter script

Fixes #2662

Update FlutterPlugin.groovy

Provide more documentation for MojoShell

As usual, as I was doing this I ran into some stuff that seemed hard
to document as-is and so I changed it. In this case, in the "http"
library. The new code is more or less equivalent, I think, but the
resulting documentation makes it more obvious that it's wrong...

Refactor cassowary so it uses imports rather than parts.

Improve flutter create help text.

Also misc cleanup:
 - reorder members to be more consistent and fit the style guide
 - remove use of _Pair
 - made Variable.applyUpdate and Variable.owner public
 - added docs to Priority, tweaked the code a bit
 - added some docs to Result
 - removed the internal-error Result (replaced with asserts)
 - removed unused Results
 - made Result const
 - merged some files together since they had used privates a lot

I'm sorry this is completely unreviewable. I did the move from `lib/*`
to `lib/src/*` first, then did the `part`-to-`import` change, and then
found out how many of the files involved privates, which I wasn't
expecting. I can redo this as multiple commits if that would make it
easier to review.

Track metrics for RepaintBoundary.

Fixes https://github.com/flutter/flutter/issues/475

Update the groovy build example.

Refactor CheckedModeBanner into something more reusable.

Replace WidgetError and RenderingError with FlutterError

Add dartdoc for child widgets

This patch adds a consistent, simple description for the common pattern of
having a single child widget.

Docs for AvatarCircle.

[driver] actually start the timer when connecting

Tweak the selected tab indicator animation.