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This patch fixes a problem with throttled FrameViews sometimes appearing partially painted.
This was because we generally paint some distance beyond the viewport, i.e., covering the
entire interest rect. FrameViews which are inside the interest rect but outside the viewport
are skipped during painting, so the recorded display list won't include their contents. If
the FrameView is then scrolled on-screen without causing any other paint invalidations, the
display list won't get updated and the FrameView contents will not be shown.

This patch fixes the problem by forcing a repaint of FrameViews when they become
unthrottled, discarding any previous display lists and tile textures for the area they
cover.

BUG=562343

Review URL: https://codereview.chromium.org/1603983002

Cr-Commit-Position: refs/heads/master@{#371517}