Fix FenceTracker releaseFence

This patch:
* Fixes the release fence when GPU compositing.
* Stores the final release fence in ConsumerBase just
    before releasing the Buffer, which helps ensure
    sync points aren't added unknowningly.
* Makes HWC2 release pending buffers as the first step
    of postCompostion, rather than the last, which should
    allow dequeue to unblock a little earlier and helps
    make sure the previous buffer's release fence has
    been finalized before FenceTracker::addFrame is
    called.
* Fence tracker only sets the release fence once it
    has been finalized so it does not report a release
    fence for a buffer that is still latched.

Test: adb shell /data/nativetest/libgui_test/libgui_test
--gtest_filter=*GetFrameTimestamps*

Change-Id: I27d484bfd48f730bdcea2628f96795c6f4b4df7b
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 20c0261..4772fc1 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -2173,7 +2173,7 @@
 #endif
     *outRequestedPresentTime = mSurfaceFlingerConsumer->getTimestamp();
     *outAcquireFence = mSurfaceFlingerConsumer->getCurrentFence();
-    *outPrevReleaseFence = mSurfaceFlingerConsumer->getPrevReleaseFence();
+    *outPrevReleaseFence = mSurfaceFlingerConsumer->getPrevFinalReleaseFence();
 }
 
 std::vector<OccupancyTracker::Segment> Layer::getOccupancyHistory(