Added a section which explains how to get `dart:ui` changes.

Add a --pause-isolates-on-start flag to the flutter mojo content
handler to match the one that's supported by the dart mojo content
handler.

Fixes: https://github.com/flutter/flutter/issues/4802

These classes now use the same terminology and work in the same way.
Also, change semantics.mojom to use an enumeration of actions instead of
having a separate method per action. This will hopefully scale better.

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

Avoid re-entering the message loop while reloading. Fixes on stack reloading in Flutter embedder. (#2775)

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

Fixes #69

It's empty and is easily confused with onPostResume

This will make it simpler to write listeners that can be reused in multiple
applications.

I noticed this while doing the libjpeg_turbo roll.

* 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.

Fix leaky descriptor in dart_init and use the correct macro to handle EINTRs on close syscall wrappers. (#2765)

* Use IGNORE_EINTR instead of HANDLE_EINTR when using the `close` syscall wrapper.
* Don't leak the file descriptor used to memory map Dart related artifacts.

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.

These files are generated to different paths now.

The upstream mojo.git no longer contains this code.

iOS: Discard the depth and stencil attachments of the framebuffer before presenting the color renderbuffer. (#2737)

- [x] Wire up synchronous script reloading in the library tag handler.
- [x] Allow glfw sky_shell to start from dart source as well as bundle.

This patch moves the remainder of painting and compositing into their
new home (and updates their style to match Google C++ Style).

This should make almost every Canvas call significantly faster.

These parts don't depend on engine anymore. Also reformat them to match Google
C++ style.

This patch moves the geometry classes.

Because we're not using array buffers to marshall the vertex data for
drawVertices and drawAtlas, we need to process the paint argument first so that
we don't call Dart_GetField after creating a view into an array buffer.

* Implement Canvas.drawPoints

This enables drawing polygons faster than using Paths.

Fixes https://github.com/flutter/flutter/issues/92

* Implement more Path functions

Path.fillType
Path.addPolygon
Path.addPath
Path.extendWithPath
Path.transform

Fixes https://github.com/flutter/flutter/issues/252

The only remaining calls to Dart_GetField are for Paint, which will be
handled in a later patch.