- Create a FlutterErrorDetails struct-like class that describes an

  exception along with more details that aren't in the exception, like

  where it was caught and what was going on when it was caught.



- Provide a FlutterError static API for handling these objects:



  - FlutterError.onError which is called whenever Flutter catches an

    error.



  - FlutterError.reportError() which handles an error.



  - FlutterError.dumpErrorToConsole() which is the default behavior

    for onError.



- Removes all the existing exception handler callbacks.



- Replaces all the existing places that described exceptions using

  debugPrint with calls to FlutterError.reportError().



- Extend lockState() to also catch exceptions, so that we catch

  exceptions that happen during finalizers.



- Make the test framework catch errors and treat them as failures.



- Provide a mechanism to override this behavior in the test framework.



- Make the tests that used to depend on the exception handler

  callbacks use this new mechanism.



- Make pump() also support the phase argument.



- Improve some tests using these new features.



Fixes #2356, #2988, #2985, #2220.

For example, to implement backdrop blur effects.

[driver] utility for extracting and saving timeline summary

This way, widgets that try to use the DefaultTextStyle don't have to

handle the case where there isn't an explicit default.

Turns out card_collection had all kinds of bugs.

Initial version of complex layout performance test

Tweak the typography demo to match the spec more

Previously we weren't padding the top and the bottom of drop-down menus but the

spec says these should have 8.0 pixel of padding, the same as popup menus.



Fixes #2683

Support "flutter refresh" in the Gradle-based sample project

* sort imports

Polish selection controls

Leave all entered targets when finishing.

pubspec normalization; remove den

Capture closures around megamorphic dispatches

The performLayout and build callsite are highly megamorphic because they
dispatch into a large number of clients. However, for a given caller, the
callee is always of the same type, which means the megamorphic lookup exactly
factors by the caller. We can speed up the dispatch by capturing a closure at
initialization and then monomorphically dispatching through the closure.

Add a scrolling test now that it passes

Update engine version

Don't delay between dismissing a snack bar and the next snack bar

Update engine

Previously, the Dismissable widget was animating down to zero width off
screen. Now, we tell it to skip the resize animation.

Fixes #3030

Add review feedback to dartdocs

Fix broken link in the docs

Drop is a separate word than down

We fixed this issue a different way but the test is still valuable.

[driver] switch to different pause event workaround

Fix spinning_mixed widget example, plus minor style fix

Improve setState-after-dispose error message

We now explicitly mention the possibility of a memory leak.

Fixes #2978