GpuStats: tighten the triggers to send GPU stats to gpuservice

Before:
(1) Any driver gets loaded and GraphicsEnvironment setup
(2) At least one activity launched and GraphicsEnvironment setup
(3) Target stats collected

After:
General pre-condition: at least one activity has been launched and
GraphicsEnvironment setup is not skipped.
(1) Any driver gets loaded
(2) At least one activity launched
(3) Target stats collected

Test: adb shell dumpsys gpu
Change-Id: Iba714e6c98d90bf9a21abdbdc2067e834a306cc2