## Description
As the related issue refer, the application may be doing too much work on its main thread even in a simple hello_world demo.
That is because the creation of `Engine` on the ui thread takes a noticeable time, and it is blocking the platform thread in order to run `Shell::Setup` synchronously.
The cost of `Engine`'s constructor is mainly about the creating of root isolate. Actually, there used to be another time-consuming process, the default font manager setup, which was resolved by https://github.com/flutter/engine/pull/18225.
Similar to https://github.com/flutter/engine/pull/18225, this pr move the creation of root isolate out from creating `Engine`. After this action, the main thread blocking is quite an acceptable slice.
## Related Issues
https://github.com/flutter/flutter/issues/40563 could be resolved by this pr.
This is a Fuchsia-only shell test, confirming that when the timezone
setting is changed on the realm via Fuchsia's FIDL interface
`fuchsia.settings.Intl`, the Dart isolate running in that realm receives
the change and starts reporting the appropriate timestamp.
We already have a [similar test][tst] that verifies the timezones in the
dart VM matches the local timezone at start, but there was no test that
also verified timezone changes.
[tst]: https://github.com/flutter/engine/blob/master/shell/common/shell_unittests.cc#L1166
See issue #61284
Reland #19396 with a fix for improper scale that was affecting internal tests
Tested: Ran all unittests, ran internal tests, and ran workstation on Fuchsia
BUG: 53062, 53063
The fuchsia code around metrics and sizing was just sending this
information through a side-channel, when the engine already had the
information available. So, delete all of it to make future CLs simpler.
Additionally, the SceneUpdateContext has many unneccesary dependencies
re: metrics and PaintTasks. Break those to make future CLs simpler.
Tested: Ran all unittests and ran workstation on Fuchsia
BUG: 53062, 53063
This is part of a larger effort to expose the difference between GrDirectContext,
which runs on the GPU thread and can directly perform operations like uploading
textures, and GrRecordingContext, which can only queue up work to be delivered
to the GrDirectContext later.
* [fuchsia] fix Rasterizer::ScreenshotLayerTreeAsPicture on Fuchsia
* [fuchsia] Add shell test for skp based shader warmup
* [fuchsia] use custom image serialization when writing out SKP's
This change adds custom image serialization functions for skp serialization
which write out onlythe image metadata and not the contents of the
images themselves. This allows SKP's to be used for shader warmup with
a significantly reduced disk space footprint.
Tweak the primary flutter build rule so that fuchsia is more similar to
other platforms in how tests and the shell are built.
Only embedder_unittests and GLFW tests are disabled on Fuchsia now.
TEST: Ran unittests on host/fuchsia; workstation on fuchsia
BUG: fxb/53847, fxb/54056
