This reverts commit d43d3534.

Clear regression to the flutter_gallery_ios__transition_perf benchmarks:
  * average_frame_build_time_millis: 1.4x
  * missed_frame_build_budget_count: 1.2x

No regression seen for other iOS benchmarks (e.g. scrolling).

* Switch from FlutterFastaTarget to FlutterTarget as FlutterFastaTarget was removed.

* Change to new SkFontMgr API

These changes clarify ownership rules and work today. They will be
necessary once SK_SUPPORT_LEGACY_FONTMGR_API goes away.

* Fix spacing

* Formatting

When checking whether render buffer size has changed, apply the device
scale factor used to convert points to pixels to ensure we're not
needlessly re-allocating render buffer storage.

Adds trace + debug log to make this easier to detect in future.

Originally introduced in 2d530dae, but
rolled back in 0a6e415b to test whether
it was responsible for regressions to
flutter_gallery_ios__transition_perf benchmarks:
  * average_frame_build_time_millis
  * missed_frame_build_budget_count

This reverts commit 0d2f0cb6.

Attempting to roll into the framework causes analysis errors with
mock classes implementing HTTP-related classes previously in dart:io:
[error] Classes can only implement other classes. (packages/flutter_tools/test/base/net_test.dart, line 94, col 41)
[error] Classes can only implement other classes. (packages/flutter_tools/test/base/net_test.dart, line 62, col 33)
[error] Classes can only implement other classes. (packages/flutter_tools/test/base/net_test.dart, line 78, col 40)
[error] Classes can only implement other classes. (packages/flutter_tools/test/src/context.dart, line 249, col 46)

and dartdoc failures:
dartdoc:stdout: [error] Target of URI doesn't exist: 'dart:_http'. at /home/travis/build/flutter/flutter/bin/cache/pkg/sky_engine/lib/io/io.dart, line 206.

- Remove linking of dart_debugger.cc as this is not used
(all debugging is done using the service API, this debugger implementation uses the deprecated dart debugger API)

* Revert "libtxt: handle characters encoded as multiple UTF-16 code units (#4165)"

This reverts commit 414c3fe3.

* Revert "Proper horizontal a11y scrolling on Android (#4163)"

This reverts commit 0448bf9b.

* Revert "Update Skia revision to 74a8296d7c. (#4164)"

This reverts commit ac53d29a.

* Revert "Revert "Revert engine Dart roll. (#4158)" (#4162)"

This reverts commit f97e974e.

This reverts commit 14aab33e.

e1aa8673 fixes issue with last dart
roll.

This is required by the _CryptoUtils class used by the recently repackaged
Dart HTTP libraries

* Revert "Include _http into sky_engine libraries for analyzer (#4154)"

This reverts commit b930f107.

It is dependent upon the Dart roll, which breaks the engine.

* Revert "Roll dart to ade37f931e90b0fdb8fe16d6bf6f089545da55b6 (#4151)"

This reverts commit 6f1264fb.

This Dart roll breaks the engine build on Travis.

Adds support for system text scale factor, including hooks for Android system settings changes.  iOS hooks will be added in another PR.

libtxt: Remove postprocess_line and improve tracking of X offsets for glyphs and PaintRecords (#4153)

* Roll dart

* Update dart dependencies

* Update dart license hash. No changes to licenses

* Roll to one more version up

* Update license hash

* Add overlaps method to Rect

* review comment

See https://chromium.googlesource.com/chromium/blink/+/24cf1f3562a59a0e397ada4a4b619494f038f368

Fixes https://github.com/flutter/flutter/issues/12280

These libraries are in Topaz now.

This addresses part of #8028, implementing the Engine-side support for it.

Use fuchsia specific extension to avoid casting handles as fds.

Previously, cases like:

```dart
Color.lerp(const Color(0xFF00FF7F), const Color(0xFF00FFFF), 1.1)
```

...would result in unexpected effects (in this instance, lerping
between these colors with a curve that overshoots would take what
should be a simple animation from pale green to blue and add some
flickering bright green whenever it overshoots).

This reverts commit 513828b5.

This breaks linux build due to outdated pool dependency in observatory pub packages.

* Roll dart dependency to 24ad1035147b65dd42e765b566f5002e87caafa7

* Update dart license hash(no relevant changes). Update dart deps.

It's not an error to be unable to connect to the context service.

Fixes https://github.com/flutter/flutter/issues/12235