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/SurfaceFlingerConsumer.cpp b/services/surfaceflinger/SurfaceFlingerConsumer.cpp
index 6f2520b..5317cc7 100644
--- a/services/surfaceflinger/SurfaceFlingerConsumer.cpp
+++ b/services/surfaceflinger/SurfaceFlingerConsumer.cpp
@@ -189,10 +189,14 @@
     return nextRefresh + extraPadding;
 }
 
+sp<Fence> SurfaceFlingerConsumer::getPrevFinalReleaseFence() const {
+    Mutex::Autolock lock(mMutex);
+    return ConsumerBase::mPrevFinalReleaseFence;
+}
+
 #ifdef USE_HWC2
 void SurfaceFlingerConsumer::setReleaseFence(const sp<Fence>& fence)
 {
-    mPrevReleaseFence = fence;
     if (!mPendingRelease.isPending) {
         GLConsumer::setReleaseFence(fence);
         return;
@@ -222,17 +226,8 @@
             strerror(-result), result);
     mPendingRelease = PendingRelease();
 }
-#else
-void SurfaceFlingerConsumer::setReleaseFence(const sp<Fence>& fence) {
-    mPrevReleaseFence = fence;
-    GLConsumer::setReleaseFence(fence);
-}
 #endif
 
-sp<Fence> SurfaceFlingerConsumer::getPrevReleaseFence() const {
-    return mPrevReleaseFence;
-}
-
 void SurfaceFlingerConsumer::setContentsChangedListener(
         const wp<ContentsChangedListener>& listener) {
     setFrameAvailableListener(listener);