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.

Currently fCanvas is invalid during flushPendingCommands reason for which is
currently being debugged. An extra setPlaybackCanvas() is currently being added
in flushPendingCommands() as a workaround since fCanvas.