Bug 906427 - When a touch event has multiple touch points, send it to the root APZC for the layer subtree. r=
Bug 907977 - Don't null out the mApzcForInputBlock prematurely. r=
Bug xxxxxx - Add some APZC_LOG debug logging to AsyncPanZoomController.cpp
Turn on logging
Bug 906877 - Remove code obsoleted by multi-apzc. r=

Now that we have multi-APZC landed, we don't need BrowserElementPanning
to detect when it's about to scroll a subframe and let APZC know. So
the two messages involved in this can be completely removed.
Bug 885023 - Convert mFrameMetrics.mZoom to a CSSToScreenScale. r=

The mFrameMetrics.mZoom was previously a "resolution-independent" zoom,
which meant it had to always be multiplied by the CalculateIntrinsicScale()
value to be useful. This patch converts it to a "resolution-dependent" zoom,
and includes the intrinsic scale multiplier already. This means it needs
to be updated if either the viewport or composition bounds (which determine
the intrinsic scale) change, but there are only a few places where this
happens and it makes the rest of the code cleaner.