Bug 981029 - Make ProcessUpdateFrame behave in less magical ways. r=botond

Replace the always-true return value, with a FrameMetrics object that
reflects the final metrics put in place. Also remove the side-effect of
assigning mLastRootMetrics and put that in the call sites instead.
Bug 981029 - Change the GeckoContentController interface to take CSSPoint instead of CSSIntPoint. r=botond
Bug 981029 - Fix the LD transform so that the translation component is in layer pixels. r=botond
Bug 981029 - Save and apply an input transform to input events from the APZ. r=botond

This accounts for the fact that in some cases we may not apply all of the
requested paint metrics from the APZ, leaving the two sides of the
GeckoContentController interface out of sync (on purpose).