Bug 1048667 Part1: silk preference
Bug 1048667 Part2: vsync event protocol
Bug 1048667 Part3: vsync dispatcher framework
Merge branch 'silk-Bug-1048667' into silk-vsync-dispatcher-framework

Conflicts:
	dom/ipc/ContentParent.cpp
	gfx/layers/ipc/VsyncEventChild.cpp
	gfx/layers/ipc/VsyncEventParent.cpp
	widget/gonk/GonkVsyncDispatcher.cpp