modules: camera: Shutter notify message support

The shutter callback timestamp should originate from the sensor itself,
since it knows exactly when the first line of the frame started
exposing.  However, as a fallback (or in the CPU-painting case) query
CLOCK_BOOTTIME instead.

Change-Id: Id57c05525e9c575d009b9deb96a69557fccac16b
diff --git a/modules/camera/Camera.h b/modules/camera/Camera.h
index c7ee52d..16e1439 100644
--- a/modules/camera/Camera.h
+++ b/modules/camera/Camera.h
@@ -72,6 +72,8 @@
         // Process an output buffer
         int processCaptureBuffer(const camera3_stream_buffer_t *in,
                 camera3_stream_buffer_t *out);
+        // Send a shutter notify message with start of exposure time
+        void notifyShutter(uint32_t frame_number, uint64_t timestamp);
 
         // Identifier used by framework to distinguish cameras
         const int mId;