Bug 905909 - Avoid infinite recursion in nsTreeBodyFrame. v1

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extra : rebase_source : ed9efcd923249d5c7efebf9185ea431140878efc
Bug 918185. When Range.getBoundingClientRect/getClientRects needs a textframe for a node, create one if the textframe was optimized away. r=bz
Bug 905405. Wrap mLastNativeEventScheduled in a mutex to avoid racing on it. r=bsmedberg