Fix getFrameTimestamp test flakes.

This fixes both the dEQP CTS flakes relating to
compositor timing and the lib_gui test flakes that
don't initialize properly.

Test: adb shell /data/nativetest/libgui_test/libgui_test
  --gtest_filter=*GetFrameTimestamps*
Bug: 35995043

Change-Id: If8e59f0dc9a916bab28bd1a36190cef9a56cb64f