Contains the following changes:

d80c1de7b (HEAD -> master, upstream/master) Roll src/third_party/skia ab3144c3abb9..656cefe65d62 (11 commits) (#6362)
edf6249e0 Add pushOffset to SceneBuilder (#6349)
3a01f3956 Change log level from ERROR to WARNING (#6361)
5ae470845 Roll src/third_party/skia 227d4e10276c..ab3144c3abb9 (11 commits) (#6360)
763627fff Do not export libdart symbols (#6337)
3052dbd79 SystemNavigator.pop can pop w/o UINavigationController (#6341)
0c096f798 Roll src/third_party/skia b3e48afc936d..227d4e10276c (1 commits) (#6359)
b8c2a17a1 Roll src/third_party/skia cfe1264d7465..b3e48afc936d (3 commits) (#6356)
c589b312a Expose push/popRoute on FlutterViewController (#6347)
075b3fcca Roll src/third_party/skia 5ea41fc89b26..cfe1264d7465 (1 commits) (#6355)
2dd9b99aa Roll Dart to version 808ed6238b9262660e31ea826f7aea6cfa3a3493 (#6354)
5b799381f Dont make any binaries specify an X11 dependency. (#6353)
309ac4e1b V0.8.2 fix compile problem with xcode10 (#6339)
26fdd1e4f Roll src/third_party/skia 5767fc042834..5ea41fc89b26 (3 commits) (#6351)
cc44ca5d0 Perform persistent cache stores on the IO thread outside the frame workload. (#6350)
f2a3df97e Wire up the Skia persistent GPU related artifacts cache. (#6278)

* enable lint unnecessary_new

* fix tests

* fix tests

* fix 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

Fixes https://github.com/flutter/flutter/issues/11539

* Do not lower-case paths during canonicalization.

This breaks hot reload on some platfroms with case insensitive file systems.

* Add unit tests

It was resulting in weird situations where the tool would dump an
error message and stack but not quit, or would fail hard but then just
hang.

Instead, specifically catch errors you expect. As an example of this,
there's one error we expect from the DartDependencySetBuilder, so we
catch that one, turn it into a dedicated exception class, then in the
caller catch that specific exception.

`all.dart` is no longer needed. Furthermore, it causes tests to
be skipped, or to silently fail to run anything.

Fixes #7941

This implements the `DartDependencySetBuilder` completely in Dart instead of calling out to `sky_snapshot` (Linux/Mac) or `gen_snapshot` (Windows) and allows us to use the same code path on all supported host platforms.

It also slightly reduces hot reload times on Linux from ~750ms to ~690ms for the unchanged flutter_gallery app and significantly reduces hot reload times on Windows from almost 1.5s to just slightly slower than on Linux.

This change will also allow us to retire `sky_snapshot` completely in the future.

* Enable Hot Reload on Windows (backed by gen_snapshot)

\o/

Two caveats:
* Hot Reload on Windows is slower than on other platforms because gen_snapshot is slower then sky_snapshot
* We currently cannot hot reload projects with spaces in the path

* enable tests

* Revert "Revert "Simplify path handling logic in dependency checker and devFS (#8414)" (#8467)"

This reverts commit 96ba7f76.

* Intentionally use a self-package URI in flutter_gallery

* tests to catch problems with self-package imports

This reverts commit e7bde11c.

Reason: broke hot reload when using "package:" style imports for sources
within the same project.

* Simplify path handling logic in dependency checker and devFS

Simplification will make it easier to port this to Windows.

* Roll Engine to 0a7b177c330367904597a6129b3eb653d29dfca0

This ensures that accidental usages of dart:io's
file API don't creep in over time.

- [x] Introduce DependencyChecker which can determine if any dependencies have been modified.
- [x] Move the DartDependencyBuilder into a separate file.
- [x] Add unit tests for DartDependencyBuilder.
- [x] Add unit tets for DependencyChecker

Part of #7014