Transfer HWC release fences to BufferQueue

After a HWC set, each SurfaceFlinger Layer retrieves the release fence
HWC returned and gives it to the layer's SurfaceTexture. The
SurfaceTexture accumulates the fences into a merged fence until the
next updateTexImage, then passes the merged fence to the BufferQueue
in releaseBuffer.

In a follow-on change, BufferQueue will return the fence along with
the buffer slot in dequeueBuffer. For now, dequeueBuffer waits for the
fence to signal before returning.

The releaseFence default value for BufferQueue::releaseBuffer() is
temporary to avoid transient build breaks with a multi-project
checkin. It'll disappear in the next change.

Change-Id: Iaa9a0d5775235585d9cbf453d3a64623d08013d9
diff --git a/services/surfaceflinger/DisplayHardware/HWComposer.h b/services/surfaceflinger/DisplayHardware/HWComposer.h
index 05c6f6d..cb4c2db 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.h
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.h
@@ -100,6 +100,7 @@
     public:
         virtual int32_t getCompositionType() const = 0;
         virtual uint32_t getHints() const = 0;
+        virtual int getAndResetReleaseFenceFd() = 0;
         virtual void setDefaultState() = 0;
         virtual void setSkip(bool skip) = 0;
         virtual void setBlending(uint32_t blending) = 0;