[driver] add smoke driver test; find by tooltip; retry predicate

Point Stack users to CustomMultiChildLayout.

Teach flutter logs to show only new logs

Remove unused updater package.

After this patch, the flutter logs command on Android shows only log messages
since the command was run. Previously, it showed historical logs, which was
confusing.

Fixes #2013

Fixed a typo - Expland

Show time deltas

add back a call to device.stop() from the run command

update to CONTRIBUTING.md to use the new update-packages command

improve startup time

flutter analyze: handle missing files

SizeObserver crusade: The Last Test

SizeObserver crusade: ScrollableMixedWidgetListState

Handle lines getting shorter during analysis

SizeObserver crusade: Mimcable

Disabled IconButtons render correctly

Remove AnimationDirection

Fix crash in Block.

Elide fewer AnimationStatus callbacks

This concept is now private to AnimationController. All the clients actually
want the AnimationStatus.

Previously we would elide forward and reverse callbacks that canceled each
other out, which broke the expected state machine. Now we synchronously deliver
status callbacks when start an animation.

Fixes #1913

Stop animating in deactivate()

This assert was overzealous. You can update a RawGestureDetector any
time before the semantics phase, it doesn't have to only be during your
child's layout.

This is good because Block has additional PointerListeners between its
GestureDetector and its Viewport.