Track frame events incrementally and per layer.

* Replaces FenceTracker, which was owned by SurfaceFlinger,
    with FrameEventHistory, which is owned by Layer.
* Updates FrameEventHistory as events occur.
* Changes SurfaceFlinger flag "--fences" to
    "--frame-events".

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

Change-Id: I868c2ef93964656d7e41848243433499e7f45fe7