Add a DequeueReady FrameEvent

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

Change-Id: I98ffd4123fc50b5f560e432f4078408c913c8edf
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 193b702..23c4b30 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -1226,8 +1226,9 @@
     ALOGV("postComposition");
 
     // Release any buffers which were replaced this frame
+    nsecs_t dequeueReadyTime = systemTime();
     for (auto& layer : mLayersWithQueuedFrames) {
-        layer->releasePendingBuffer();
+        layer->releasePendingBuffer(dequeueReadyTime);
     }
 
     const sp<const DisplayDevice> hw(getDefaultDisplayDevice());