* Added the superellipse (a.k.a. squircle) shape to flutter, which is needed to recreate some cupertino components, e.g. buttons in pixel-perfect detail (issue #13914).

* Ensure all errors thrown by image providers can be caught by developers.

Add an `onError` parameter to the ImageCache.putIfAbsent method.
In the event that an error is thrown when resolving an image, catch if
this parameter is provided. Use the onError parameter to ensure that all
errors thrown are forwarded to the ImageStream error channel instead of
directly into the void.

* Fix bug in calculation of downstream text distance when aligned: right

* After having affinity explained to me, match getOffset and tests to
expected behavior

* Clean up test formatting and fix analyze errors

* Improve test comments and reorganize a bit

* Specify logical pixels

Fixes https://github.com/flutter/flutter/issues/24257

This re-lands 3c56e6c7 on top of a new Dart SDK that contains new mixin syntax fixes.

* Add support for shadows in text.

* Use dart:ui Shadow as base class for Shadows

* Update lerp definition

* Roll engine 3ffa3629523..84fe4a9f7e24e4 - Text Shadows and update goldens for skia roll.

git log 50c2e69daff4e207c54e463d2304139985c7511c..32f417db0d566d354605305cb29c251276fa65ee --oneline --no-merges
32f417db0 Roll tonic to 077be256142ede39a271385907faadf4fcc62a4d. (#6541)
4ee77256c Revert "Roll Dart to 1f4dfce179c8f05c9e48759300a15e671b88cc10 (#6515)" (#6537)
964acafeb Roll src/third_party/skia 646d917d3c71..c6a17104ad68 (1 commits) (#6536)
d4bae4ca4 Roll src/third_party/skia 2b2c00f6ec36..646d917d3c71 (1 commits) (#6535)
ff93ccf47 Roll src/third_party/skia 681692726fc0..2b2c00f6ec36 (1 commits) (#6534)
a4161c895 Roll src/third_party/skia 23775a2e9736..681692726fc0 (1 commits) (#6532)
116072e46 Roll src/third_party/skia 7435f2553f53..23775a2e9736 (1 commits) (#6531)
ef0b0f6e9 Roll src/third_party/skia bc7a51e79c5b..7435f2553f53 (1 commits) (#6530)
f46b7b971 Roll src/third_party/skia b28db529c866..bc7a51e79c5b (1 commits) (#6529)
9033c3902 Roll src/third_party/skia 7e67041a1428..b28db529c866 (1 commits) (#6528)
e6887a412 Add missing imports for unicode/utf16.h (#6524)
1242f6dfe Roll src/third_party/skia d38382d060ca..7e67041a1428 (2 commits) (#6527)
a1bbea77c Add a no-op platform view layer. (#6505)
2bb3afad8 Roll src/third_party/skia 21bd60daa3f3..d38382d060ca (10 commits) (#6526)
75e875240 Fix the Mac embedder build (#6525)
436f9707b Add version check for dismissable (#6522)
7767c785b Provide a default GL function resolver in the embedder (#6523)
32841dd89 Case-insensitive matching of family names for custom fonts (#6519)
a9076c7e6 Roll src/third_party/skia 419709dbb167..21bd60daa3f3 (11 commits) (#6520)
f2e7441b5 An API for loading fonts from a buffer provided by the application (#6508)
05aac0f27 fix ResourceExtractor npe. (#6461)
cf5a2a145 Roll src/third_party/skia b27a9cf2f4a8..419709dbb167 (16 commits) (#6517)
84fe4a9f7 Re-revert invalid line height tests (#6516)
5f529566c Add support for text shadows (#6385)
e44c10c96 Reland "Share engine layers with the framework" (#6412) (#6468)
ba0449971 Roll Dart to 1f4dfce179c8f05c9e48759300a15e671b88cc10 (#6515)

Users can set `PaintingBinding.decodedCacheRatioCap` to control the max
amount of memory used per image to avoid decoding frames each animation
loop.

This depends on flutter/engine#6310.

Fixes #20998, and fixes #14344

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* Scale high-pixel-ratio images with BoxFit.none/BoxFit.scaleDown correctly

* add test cases for image scale

* make analyzer happy

* Make sure that test images always have a scale to make all tests pass

* add a new author

* use new keyword in tests

* Upgrade everything except matcher.
* Roll matcher (and test)
* Adjust tests that depend on flutter:test directly to depend on a shim
* Require use of package:test shim and remove other references to package:test

It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

Move the notch computation from the FAB to the BAB.

The notch in the BAB (bottom action bar) for the FAB (floating action button) was previously kept as part of the FAB's implementation. This was done to keep the shape of the FAB and the shape of the notch coupled.
That approach resulted in a somewhat complex and 'non Fluttery' mechanism for propagating the notch computation from the FAB to the BAB.

This CL uncouples the FAB and the notch computation.
With the new API the BAB computes its overall shape including the notch using a NotchedShape delegate.

This includes multiple breaking changes:
  * Scaffold.setFloatingActionButtonNotchFor is deleted.
  * The ComputeNotch type is deleted.
  * The hasNotch property of BottomAppBar is deleted.
  * The notchMargin property of FloatingActionButton is deleted.

Quick migration guide from the previous API:

| Previous API | New API |
| ------------------|-------------|
| BottomAppBar(hasNotch: false) | BottomAppBar() |
| Using a FloatingActionButton with: BottomAppBar() / BottomAppBar(hasNotch: true) | BottomAppBar(shape: CircularNotchedRectangle()) |
| Scaffold.setFloatingActionButtonNotchFor(..) | No longer supported |

* update tests for TextStyle changes in engine

* roll engine, support Foreground on TextStyle

* roll to TextStyle.foreground

* add tests, update docs, fixes from tests

* add golden tests

* stroke + gradient

* update goldens hash

* Use centered widget

* fix typo

* Disable golden tests until Linux generated files are available

* update goldens

The new matcher package deprecates isInstanceOf which seems eggregious.

This adds an HSLColor class which uses a perceptual color space based upon human perception of colored light (as opposed to HSV, which is based on pigment colors).

You can see the difference in the color spaces here: https://en.wikipedia.org/wiki/HSL_and_HSV

I also added a "within" matcher for both HSLColor and HSVColor that will check if the (floating point) color components are within a certain error.

And tests.

* update tests for TextStyle changes in engine

* roll engine, support Foreground on TextStyle

* Support for saving Dart compilation trace on device

* Expose Gradient.radial

* cleanup doc

* update tests, null check

* add asset images

This PR adds a SweepGradient class, extending Gradient to expose the engine's ui.Gradient.sweep shader.

Similar to LinearGradient and RadialGradient - SweepGradients can be used in a BoxDecoration or passed to a Paint's shader.

When passing a Color object with same R/G/B code ( e.g. [new Color.fromRGBO(100, 100, 100, 1.0)] ) to HSVColor.fromColor(Color color) , the hue in return will be NaN .