- [x] Fixes devfs opening too many files.
- [x] Build fixes related to Fuschia support

Remove dependencies on ui, third_party/mesa and mojo/convertors. Provide simple alternatives. (#2783)

- Pick up fix for 64-bit AOT/caching-JIT snapshots.

- clustered serialization (dart-lang/sdk@524fbc1e0f9d61ff5da69bbed2b35745528de945)
 - background finalization (flutter/flutter#3804)

https://github.com/flutter/flutter/issues/4560

* Update to mojo fd8d18dbf7a4f9ed8a607648cca6d2c595b1c580

* Update mojo_sdk

* Update to account for Mojo API changes

* Backport to older base

* Update libjpeg_turbo

* Update our libjpeg_turbo BUILD.gn file

This brings in this file from upstream:
https://chromium.googlesource.com/chromium/src/+/master/build/secondary/third_party/libjpeg_turbo/BUILD.gn

* We don't always build with libjpeg

...so the libjpeg target isn't always available.

Updating base turns out to be more complicated than I thought.

This reverts commit daa822aa.
This reverts commit c38428c7.
This reverts commit 4b73a8a0.

Update base, gn, and their clients.

update Dart to get https://github.com/dart-lang/sdk/commit/6b6d363900373a56caa971b5610b3a0050ed55f6 (#2734)

* Update to mojo 7d579155cc597aa3befcbfad66eef54bda06b57c

* Update to new API

We still need this for the observatory build.

This reverts commit 5082974b.

The engine.git repo doesn't need a copy of the Dart SDK anymore.

Fixes https://github.com/flutter/flutter/issues/2618

* Update to mojo 9a791294e429f9f2ca4f427796a284edb6f6768e

* Update to account for Mojo API changes