Support SurfaceView synchronization.

Add API for fetching the next frame number to be produced by
a given buffer producer. Add an API to SurfaceComposer to 
defer execution of the current transaction until a given frame number. 
Together these may be used to synchronize app drawing and surface 
control updates.

Change-Id: I8e0f4993332ac0199c768c88581a453fefbaff1d
diff --git a/libs/gui/Surface.cpp b/libs/gui/Surface.cpp
index a31876b..9191b2a 100644
--- a/libs/gui/Surface.cpp
+++ b/libs/gui/Surface.cpp
@@ -111,6 +111,10 @@
     return result;
 }
 
+uint64_t Surface::getNextFrameNumber() const {
+    return mGraphicBufferProducer->getNextFrameNumber();
+}
+
 String8 Surface::getConsumerName() const {
     return mGraphicBufferProducer->getConsumerName();
 }