* This allows the tests to add their own FLX files but still use consistent fonts.
* The test fonts are only embedded on the desktop test shells. The option is not available on mobile platforms.
* Right now, all fonts will resolve to the test font. If we want tests to be able to use the fonts they embed in FLX files but use the test font for platform fallbacks, we will need to add font selector fallbacks. I can do this in an another patch. So far, there are no users of this functionality.

This transport uses the Dart and JNI APIs directly instead of indirecting
through Mojo.

Add a —disable-observatory flag to explicitly disable observatory even in non-product modes. (#3012)

We used to be able to toggle observatory via a command line flag. But now, we enable or disable observatory based on the Flutter product mode.

This also allows us to fix an issue where the —non-interactive flags was being hijacked by the Dart initialization logic to enable or disable observatory. However this flag was orignally meant for the standalone runner to launch either to run tests or to run a full graphics enabled window on the desktop.

Add “—endless-trace-buffer” to switch to an endless buffer from a ring buffer while tracing. (#2966)

* Add config properties to specify snapshot blob file names.

This adds the ability of the shell to override the default
dart aot snapshot blob file names, and it wires up Android's
FlutterMain to recognize the properties in the app's manifest.

This will be used for flutter applications that build their
binary snapshots into files other than the default ones
that the engine uses.

Now lib/ui depends on sky/engine rather than the reverse.

This pulled a refactoring of how we keep track of the primary threads.