This still is very limited in what it can lerp, but it sets the stage for arbitrary lerps later.

If the flex is empty, there's no space in which to draw the overflow indicator,
so we shouldn't bother trying to draw it.

Fixes #12532

* add CupertinoIcons

* Use new font name convention

* review

This is follow-up to be1467e0.

This lets us preview widgets in the gallery using small, normal, large, and HUGE text.

Added selections to the main drawer for these options. Defaults to "normal", obviously.

Previously chosen pattern was generated in the output not quite at the end of the hot reload process.

* Restructure hot mode test so it runs interactively.

This allows to add a benchmark for hot reload after actual source code change.

* Add curly braces, refactory copyRecursive

This modifies the MaterialButton to expand vertically to fit the size of the contained child, no matter what the child widget is. It tries to be as close as possible to the minHeight constraint.

Also updated some doc comments to have headers (extra blank line after first sentence), and to wrap at 80 cols.

Addresses #12311

* Keep incremental compiler state through full restart.

* Add todo

* Add todo

(post-merge followup for #12516)

Fixes #12480

Make material slider respect textScaleFactor

Fixes #5938

Reapply "When parts of the program are changed in a hot reload, but not executed during the reassemble, warn that a restart may be needed." (#12490)

This reverts commit 5e7bcbac.

`flutter run --benchmark` was triggering a different quick bailout path in the VM than `flutter run`. The failure has been fixed upstream.

* Fix restart flow for preview-dart-2 mode.

Restart in preview-dart-2 needs to use kernel file and it has to be complete, rather than incremental kernel file.

* Add curly braces

* Do full compile on restart

* Roll engine to pick up changes to hot reload for preview-dart-2

The initial loading happens on the host, which was building a script snapshot and allowing imports of dart:mirrors. Hot reload happens on the device, which then notices the imports and issues a compile-time error. This change causes programs with imports of dart:mirrors to be rejected during the initial load.

Fixes https://github.com/flutter/flutter/issues/12440

* Keep Icon's subtree structure the same with and without a semanticLabel.

This avoids rebuilding the subtree when a semanticLabel is set/unset.
Also updated some doc comments.

(This is a followup on post-merge comments for #12475)

Fix Italian translations for CUT and COPY.

Fixes #12483

* Update Semantics for SingleChildScrollViews

* refactor

* review feedback

* added assert and comments

* doc

* Allow specifying and a11y label for Icon widget

This reverts commit e7061698.

This causes preview-dart-2 test failures.

* Roll engine

* Move assert requiring 'this' from initializer to constructor body

* Update test expected message

* Relax regexp to allow wider array of dart uris

Also:

 * Provide a better message when you lerp from infinity to finity
   constraints.

 * Make the striped marker support RTL.

 * By popular demand, dump a warning to the console the first time
   a particular Flex overflows. (Resets on hot reload.)