Compositor hit test performance improvement

When computing touch hit rects, keep track of the rect for the parent element
in the render tree.  If a child lives in the same layer and it's rect
is entirely contained by the parent (fairly common in practice), then
we can skip it.

For the sites I've found with the most hit rects (from our main telemetry
page sets), this decreases hit rect computation time by about 20-60%.

BUG=263416

Review URL: https://chromiumcodereview.appspot.com/19614004

git-svn-id: svn://svn.chromium.org/blink/trunk@155344 bbb929c8-8fbe-4397-9dbb-9b2b20218538