Early return in markContainingBlocksForLayout if selfNeedsLayout.
Early return in markContainingBlocksForLayout if selfNeedsLayout.

This is just a performance optimization. This will be useful as we get rid
of setNeedsLayout(MarkOnlyThis) calls.

Review URL: https://chromiumcodereview.appspot.com/21142005

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@155212 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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