* compare to null with ==

* address review comments

This reverts commit b07d986f.

Eliminates the --snapshot and --depfile parameters from the flutter
bundle command. The snapshot parameter is unused in Dart 2 -- code is
built to kernel .dill files and for profile/release builds, then AOT
compiled.

While depfiles are still used in Dart 2 (e.g. by the kernel compiler),
there are enough assumptions in the code that they lie in the default
location (e.g. in the Gradle build) and no reasons to support
user-cusomisation that it makes sense to eliminate the --depfile option
as well, and always use the default location.

This commit also renames 'depFilePath' to 'depfilePath' for consistency
across the codebase.

* Fix internationalization issues with cupertinoTextSelectionControls

Fixes #22247.

* Make Chip press elevation customizable.

* Change flutter tool to not require Fuchsia build args

* Restore code that was commented out.

* Fix style nits.

This also involves switching from Core JIT to App JIT snapshot, and replacing per-isolate VM snapshot with the shared VM snapshot.

For now there is no separate update bundle file, as the generated update gets packaged directly into the APK for testing purposes.

git log 2a22019a8dd8..7dc6b3a8eeef --no-merges --oneline
7dc6b3a8e Skip non-existing libflutters for symbol check (flutter/engine#6374)
0cd9ee372 Add more debug loging to symbol verification script (flutter/engine#6372)
fcb3c519b Roll src/third_party/skia b726c89ff8a8..d004e0b55c4a (1 commits) (flutter/engine#6373)
5e3d786d0 Use nm from buildtools (flutter/engine#6371)

For retained rendering, we don't want to push the offset down to each leaf layer. Otherwise, changing an offset layer on the very high level could cascade the change to too many leaves, which means that we can't retain them.

To not push the offset downwards, we simply push a TransformLayer when there's an offset. Skia has a fast path for concatenating scale/translation-only matrix so this operation should be fast (no performance regression is measured on Moto G4).

This is our first step towards https://github.com/flutter/flutter/issues/21756

Through some integration testing checks, it looks like it's possible
that connecting to a new instance of the Dart VM may fail even after the
Dart VM instance has been discovered.

This means that _getDartVm should be checked in more than just one
place.  This changes the function to return a null value in the event of
a 'well-known' exception (`HttpException` or `TimeoutException`
specifically).

As a result, code now calling _getDartVm checks for null and handles it
as appropriate, and the DartVm RPC calls are all updated with
consistent timeout params.

git log 2a22019a8dd8..9ae1c14c3515 --no-merges --oneline
9ae1c14c3 Update observatory-port default behavior description. (flutter/engine#6365)
5550fdbc2 Remove cull_rects_ from SceneBuilder (flutter/engine#6352)
75e404f39 Roll src/third_party/skia 656cefe65d62..b726c89ff8a8 (8 commits) (flutter/engine#6370)

See https://github.com/flutter/flutter/pull/22278#pullrequestreview-159230244

This reverts commit 7b2d3462.

https://github.com/flutter/engine/compare/2a22019a8dd8...51de09c7e0e1

git log 2a22019a8dd8..51de09c7e0e1 --no-merges --oneline
51de09c7e Roll src/third_party/skia 10d12834c8db..f88f49d2a52e (1 commits) (flutter/engine#6377)
c0b44bc20 Roll src/third_party/skia d004e0b55c4a..10d12834c8db (1 commits) (flutter/engine#6376)
77c30cadd make sure we dont set live regionin api level < 18 (flutter/engine#6375)
7dc6b3a8e Skip non-existing libflutters for symbol check (flutter/engine#6374)
0cd9ee372 Add more debug loging to symbol verification script (flutter/engine#6372)
fcb3c519b Roll src/third_party/skia b726c89ff8a8..d004e0b55c4a (1 commits) (flutter/engine#6373)
5e3d786d0 Use nm from buildtools (flutter/engine#6371)
9ae1c14c3 Update observatory-port default behavior description. (flutter/engine#6365)
5550fdbc2 Remove cull_rects_ from SceneBuilder (flutter/engine#6352)
75e404f39 Roll src/third_party/skia 656cefe65d62..b726c89ff8a8 (8 commits) (flutter/engine#6370)

The AutoRoll server is located here: https://autoroll.skia.org/r/flutter-engine-flutter-autoroll

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.

* fix race in devicelab concurrent hot reload

* only complete future once!

This roll contains the following changes
2a22019a8 Roll Dart to version 7f9a9feae181573cca609fd1b8760d7992176699 (#6366)
0fa159a26 Add debug info to figure out why the bots are unhappy (#6369)
e031ccef7 Add missing binding for pushOffset (#6367)

https://github.com/flutter/engine/compare/d80c1de7b53a...8176f4d3c467

git log d80c1de7b53a..8176f4d3c467 --no-merges --oneline
8176f4d3c Roll buildroot to 96d2493887daabe6877142caa8504a2f964b0e7e (flutter/engine#6364)
27f77cbef Document that all MethodChannel callbacks must be called on the main thread. (flutter/engine#6245)
e6c173392 Script to verify exported symbols on release binaries (flutter/engine#6363)


The AutoRoll server is located here: https://autoroll.skia.org/r/flutter-engine-flutter-autoroll

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.

* Add vertical divider option.

* added vertical divider

* restored hello world

* final changes

* a few changes

* comment fixes

* added VerticalDivider

* few changes

* comment changes:

* ultra nits

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)

This reverts commit 1eb38abd.

Improve Swift usage in platform_channel_swift some more

Make a bunch of changes that willlarche requested in
https://github.com/flutter/flutter/pull/21712:

* Use `static let` within `enum` namespaces for String constants.
* Use `guard` for early exits and to avoid forced unwrapping.
* Explicitly qualify a selector.
* Fix a retain cycle by using a weak reference.

This reverts commit 11350fed7f9d2088232354a131ca35a6e0aa6307.

https://github.com/flutter/engine/compare/38a646e14cc2...9d4b80a60cb5

git log 38a646e14cc2..9d4b80a60cb5 --no-merges --oneline
9d4b80a60 Roll src/third_party/skia 17282da3aa94..5767fc042834 (8 commits) (flutter/engine#6348)
ef98dcb11 Add support for counter timeline traces from the engine. (flutter/engine#6315)
a961e96d1 Roll buildroot to pick up updated vs toolchain. (flutter/engine#6346)
d6bb59978 Fixed IsolateNameServer documentation (flutter/engine#6344)
0c854ac01 Roll src/third_party/skia bdf1431686c2..17282da3aa94 (4 commits) (flutter/engine#6345)
e394ea1dd Roll src/third_party/skia c05302bc84da..bdf1431686c2 (1 commits) (flutter/engine#6343)
bcdfc2312 Roll src/third_party/skia 5457141b011e..c05302bc84da (1 commits) (flutter/engine#6342)
a861f37f7 Pass on the new unsafe-package-serialization option (flutter/engine#6331)
5e77a1e46 Roll src/third_party/skia bd03b54cb98d..5457141b011e (1 commits) (flutter/engine#6340)
6332db875 Roll src/third_party/skia f18c297cfb74..bd03b54cb98d (1 commits) (flutter/engine#6338)
a08bc52e8 Roll src/third_party/skia 7ffa40cedbc4..f18c297cfb74 (6 commits) (flutter/engine#6336)
8247ce26b Implement restore functions on Android and iOS (flutter/engine#6322)
2ead5c06c Roll src/third_party/skia 4ef464cd3c2e..7ffa40cedbc4 (10 commits) (flutter/engine#6334)

* updated Flutter Doctor grammar

* updated messaging based on a suggestion by Greg Spencer

* grammar update