Show annotated invalidation rects in FrameViewer

Migrating this from rietveld: https://codereview.appspot.com/142540045/

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CL depends on Blink CL currently under review:
https://codereview.chromium.org/615223004/

This CL adds support for showing annotated invalidation rects from Blink
GraphicsLayerDebugInfo.
FrameViewer users can see Blink RenderObject paint invalidations, along
with its InvalidationReason.

BUG=402033
Oh, I see what this is doing.

Can you add a comment above the if statement that we only want to iterate through the invalidation rects if we don't have any annotatedInvalidation rects?