Bug 877726 - Convert FrameMetrics.mScrollOffset to be a CSSPoint. r=kentuckyfriedtakahe
Bug 877728 - Convert some CSS rects passed to Java from gfx::Rect to CSSRect. r=BenWa
Bug 877728 - Convert the scroll offset out-param to SyncViewportInfo from nsIntPoint to ScreenPoint. r=

Also deletes a bunch of dead code, and makes some variables local
variables instead of member variables since they are only used in
a single function and don't need to be persisted.
Bug 877728 - Convert a couple of nsInt* variables to LayerInt*. r=
Bug 877728 - Convert the page rect passed to SetFirstPaintViewport to LayerIntRect. r=
Bug 877728 - Make the screen render offset a ScreenPoint. r=