Show annotated invalidation rects in FrameViewer

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
Merge pull request #634 from nyaxt/ShowAnnotatedInvalidationRects

Show annotated invalidation rects in FrameViewer
Check that the scale argument of TimelineTrackView.zoomBy_ is positive
Merge pull request #636 from petrcermak/zoom_fix

Check that the scale argument of TimelineTrackView.zoomBy_ is positive