Skip dom traversal for getComputedStyle with clean render tree.
Skip dom traversal for getComputedStyle with clean render tree.

Skip traversal up the tree from the getComputedStyle node in
updateRenderTreeForNodeIfNeeded if the tree is already clean.

R=andersr@opera.com

Review URL: https://codereview.chromium.org/843733002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@188042 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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