Fix assertion failure in Document::updateLayoutTree()
Fix assertion failure in Document::updateLayoutTree()

needsLayoutTreeUpdate may change to false because
needsAnimationTimingUpdate changes to false due to timing in
VisualUpdatePending state. Advance state to StyleClean which we
expect when !needsLayoutTreeUpdate.

BUG=537456

Review URL: https://codereview.chromium.org/1411333002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#356194}

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