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https://crrev.com/581383 removed a preferred size timer and started
synchronously updating preferred sizes in DidUpdateMainFrameLayout.
This caused a performance regression because, even though layout is
up-to-date, the preferred contents size may need to be re-computed.
Script can cause many layouts per frame which was a performance
regression because many multiple preferred contents size updates are now
occurring per frame.

This patch adds a bool for if a layout occurred which may have changed
the preferred content size, and defers the update until after the
commit.

Bug: 872599
Change-Id: Idfe1ba523b1ecfdf8f959bafc2e20ef6a52487bb
Reviewed-on: https://chromium-review.googlesource.com/1172059
Commit-Queue: Philip Rogers <pdr@chromium.org>
Reviewed-by: vmpstr <vmpstr@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582708}