SurfaceTexture: add a CPU -> GL sync test.

This change adds a test to verify that proper synchronization is done
when using SurfaceTexture to use CPU generated images as OpenGL ES
textures in 'synchronous mode'.  Synchronous mode is particularly tricky
because SurfaceTexture will allow the buffer that's currently bound to
the GL texture to be dequeued.  We rely on Gralloc's lock function to
block until this buffer is no longer being used by the OpenGL ES.

Change-Id: I1c4e37f3e9d60ab9a0905a90a1f5060fda8e485c