Parallelize SkLightDeferredCanvas:

SkMutex(fCondVar1) manages recording thread and SkCondVar(fCondVar2) manages
the flush and playback thread . fCondVar2 waits in flush recording and playback
upon reading a flush command signals using fCondVar2 thereby releasing the wait.
Sample code for testing Parallelized SkLightDeferredCanvas.

This application creates two thread. One thread does draw
and flush operation. And other thread creates snapshot and displays.
In short term, first thread records and second thread plays back the
commands.