Pass -lgcc_s to sky_snapshot build.

libgcc_s is not a DT_NEEDED library; it gets loaded implicitly.
This change ensures that rpath is referenced when searching for
the so. This in turn gets the resulting sky_snapshot binary
closer to being able to run in Google's production environment.

Track whether accessibility is enabled.

If we send accessibility events when accessibility is disabled, we crash.

Make AccessibilityNodeInfos interactive.

Service vendors no longer specify the service entry point

Instead, the entry point is well known. The service name is passed as an argument to the service.

This lets you focus and unfocus a node.

Still doesn't seem to be enough to actually have the node exposed in
TalkBack. We probably need hover for that (that's next).

(Also fixes a leak for when a subtree has been disconnected; previously
we were only forgetting the top node of the subtree, not the
descendants. Thanks @krisgiesing for catching that.)

Hard to say if this actually works. We'll find out once we've filled
this out enough that you can walk the tree in Android's Talkback UI.

This exposes the actions on AccessibilityNodeInfo nodes.
It also tries to make the code that handles reloads more correct.

Roll Dart to 1.14.1

iOS: Dont strip release binaries

Dont keep the fake runner around as it fails validation when preparing release archives

Flutter<->Android accessibility bridge

This is another step towards enabling accessibility for Flutter on
Android. It exposes the semantics tree to Android's accessibility API
when accessibility is enabled.

It does not yet:
 - allow one to actually interact with the application via the
   accessibility API
 - expose the accessibility tree to touch exploration
 - implement the accessibility focus API

However, you can see the tree if you run uiautomatorviewer. It is there,
and it matches the UI. At least in Stocks. I didn't test anything else.

Pass the Mozart ViewHost into Dart

Change services to create temporary files that will be deleted by the…

Update service handler in dylib to use the Mojo C API only

Dart needs access to the ViewHost in order to create child views.

Include child scenes when uploading to Mozart

Previously we just dropped child scenes on the floor. Now we upload them
to Mozart. However, we just draw them on top of all the other content
and don't apply any clips or blends.

Make the `dynamic_service_loader` target explicitly depend on common deps for generated headers

Install Mojo system thunks in dylib loaded for dynamic service resolution

If the Sky shell process does not have an orderly shutdown, then temporary
files created by services may never be cleaned up.

The ResourceCleaner task will run at the next startup and clean up any files
that match the prefix used by Chromium's temporary file API.  Services will
now use the same prefix for their files.

use 'build --target' in the xcode project instead of --main

revving engine

Fix the mac build

Fix iOS implementation of SystemChrome after mojom updates