[SilkFramework] Bug 1048667 - vsync protocol and dispatch framework

1. move the ipc thread back to VsyncEventParent.
2. call VsyncObserver directly in vsync driver thread.
Bug 987529 - Part 1: Integrate GeckoTouchDispatcher into vsyncdispatcher

For inputdispatcher, we should always trigger it, so we call
AddObserver() only once for each multitouch sequence.
Bug 987529 - part 2: Integrate refresh driver into vsync dispatcher

Integrate refresh drivers on Chrome/Content process into the vsync dispatcher.

add pref "gfx.frameuniformity.refreshdriver-vsync.enabled" in b2g.js to turn on/off refresh driver with vsync
Bug 987529 - part 3: Integrate CompositorParent into vsync dispatcher

Call AddObserver() while we want to schedule the composition. We use non-always triggered AddObserver() for CompositorParent.

add pref "gfx.frameuniformity.compositor-vsync.enabled" in b2g.js to turn on/off compositor with vsync