DevTools: introduce DOM.getContentQuads protocol method

This patch introduces a new DOM.getContentQuads method.

This method returns content quads for the given node. In case of
inline elements this method might return multiple quads.

BUG=857308
R=dgozman

Change-Id: I347d399fd7592295e5ddc8ea1e93b16090423499
Reviewed-on: https://chromium-review.googlesource.com/1117920
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Andrey Lushnikov <lushnikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571235}
8 files changed