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In order to avoid the touch event queue keep growing when render handles
async touchmove events longer than 200ms, which is the async touchmove
interval, we keep coalesce touch moves and send the next touchmove
until passing the async touchmove interval and receive the ACK from render.

BUG=448760

Review URL: https://codereview.chromium.org/997283002

Cr-Commit-Position: refs/heads/master@{#330548}