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/services/surfaceflinger/MonitoredProducer.h b/services/surfaceflinger/MonitoredProducer.h
index 3df6f0f..4d2ed6e 100644
--- a/services/surfaceflinger/MonitoredProducer.h
+++ b/services/surfaceflinger/MonitoredProducer.h
@@ -57,6 +57,7 @@
     virtual status_t allowAllocation(bool allow);
     virtual status_t setGenerationNumber(uint32_t generationNumber);
     virtual String8 getConsumerName() const override;
+    virtual uint64_t getNextFrameNumber() const override;
     virtual IBinder* onAsBinder();
 
 private: