Ensure that a Mozart EntityNode (that corresponds
to an ExportNode) is always released on the
Rasterizer thread.

MZ-259

Compute the necessary texture resolution using more accurate scaling
information provided by Mozart scene node metrics events instead of the
device pixel ratio provided by the Mozart view properties (which we
might remove in the future).

This allows us to allocate smaller textures when a Flutter view is
being scaled down.

Fixes https://github.com/flutter/flutter/issues/9473

Apparently hittable is not politically correct.

Also, change the hit testing geometry so that we get our hits at the root.

There's no reason to present offscreen child views to Mozart.

Allow checkerboarding raster cache entries for debugging purposes (can be toggled from Dart). (#3200)

Example: $ mojo:launcher mojo:spinning_square

This patch removes the //flutter/sky/engine dependency from //flutter/lib/ui,
which lets us build the bulk of the dart:ui library without needing to build
//flutter/sky/engine.

This removes most (all?) of our dependency on base::RefCountedThreadSafe.

Also, switch over to //lib/tonic's typed data classes.

The code that draws the picture knows more about the picture (and the future)
than we do. This patch gives them a way to hint us about what's going to
happen with the picture in the future.

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

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

Now that tonic doesn't depend on anything in //sky/engine anymore, we
can move the code to a location where its dependencies are clearer.

This patch removes spurious dependences on other parts of the engine.

This patch paves the way to untangling a large amount of code from the engine.

Now we grab the underlying primative values before exiting the VM.

Particularly, add support for blur filters to implement backdrop blur effects.

We weren't correctly dividing by the device pixel ratio when asking Mozart to
present our child scene.

This patch contains Dart bindings for adding a child scene when running in
Mozart. The child scene is currently ignored, but a later patch will actually
incoporate it into the tree.

Now that the compositor doesn't have any tricky deps, we can make it a
top-level project, which saves a bunch of typing.

The shader is supposed to be drawn on top of the children as a mask. The
previous drawing code was incorrect.

We need this to implement RenderShaderMask properly. See #1155.

Also, remove compositor_options in favour of four int constants, four
bitwise ands, and a few zero-equality comparisons, since it doesn't
seem we'll need this to scale much after all.

Rather than relying upon the rects passed in from Dart, the compositor
should compute the paint bounds of layers from the cull rects of the
underlying SkPictures. This approach is better because it will handle
effects like shadows that paint outside the incorrect paint bounds we
use today (as well as shrinking around empty space).

This also extends DartClassLibrary to support multiple DartClassProviders
for different libraries

Instead, use C++ template to generate the callback trampolines and the
registration block.

Rather than using IDL code generation, we now use some template magic to
generate this code. No all the code is template-generated yet, but this
patch is a start in that direction.