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This patch makes the code more robust in that it adds a class which
automatically calls image draw finished on exit. This ensures that
any changes to the code (more early outs) won't forget to call that
function.

R=ericrk
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel

Review-Url: https://codereview.chromium.org/2256833006
Cr-Commit-Position: refs/heads/master@{#413367}