Add support for timestamps into SurfaceTexture.

Add support for timestamps into SurfaceTexture.

API addition: The timestamps are represented as nanoseconds from some
arbitrary time point. Like the SurfaceTexture transform matrix, the
timestamp retrieved by getTimestamp is for the last frame sent to the
GL texture using updateTexImage().

Camera HAL change: Expect vendors to set these timestamps using
native_window_set_buffers_timestamp().  For now, they are
autogenerated by SurfaceTextureClient if set_buffers_timestamp() is
never called, but such timing is likely not accurate enough to pass a
CTS test.

bug:3300707

Change-Id: Ife131a0c2a826ac27342e11b8a6c42ff49e1bea7