Replaced cc::SurfaceId::nonce_ with base::UnguessableToken

cc/surfaces/surface_id.h

Index: cc/surfaces/surface_id.h
diff --git a/cc/surfaces/surface_id.h b/cc/surfaces/surface_id.h
index 5be370ed3fb427249f2ec9b6428bb37984eedbce..a9018ae4abe85fb30da9c6043b106abbcc350091 100644
--- a/cc/surfaces/surface_id.h
+++ b/cc/surfaces/surface_id.h
@@ -26,17 +26,14 @@ class SurfaceId {
       : frame_sink_id_(other.frame_sink_id_),
         local_frame_id_(other.local_frame_id_) {}
 
-  // A SurfaceId consists of three components: FrameSinkId, local Id, and nonce.
+  // A SurfaceId consists of two components: FrameSinkId and local_frame_id.
   // A |frame_sink_id| consists of two components; one is allocated by the
   // display compositor service and one is allocated by the client. The
   // |frame_sink_id| uniquely identifies a FrameSink (and frame source).
-  // A |local_id| is a sequentially allocated ID generated by the frame source
+  // A |local_frame_id| is a sequentially allocated ID generated by the frame
+  // source
   // that uniquely identifies a sequential set of frames of the same size and
   // device scale factor.
-  // A |nonce| is a cryptographically secure unguessable token that makes it
-  // impossible for an unprivileged frame source to embed another frame source
-  // without being explicitly given the surface ID of that frame source from a
-  // privileged process.
   SurfaceId(const FrameSinkId& frame_sink_id,
             const LocalFrameId& local_frame_id)
       : frame_sink_id_(frame_sink_id), local_frame_id_(local_frame_id) {}