Make cc::SurfaceId unguessable

cc/quads/surface_draw_quad.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/quads/surface_draw_quad.h"
 
 #include "base/logging.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "base/values.h"
 
@@ skipping 23 matching lines @@
                    opaque_rect, visible_rect, needs_blending);
   this->surface_id = surface_id;
 }
 
 const SurfaceDrawQuad* SurfaceDrawQuad::MaterialCast(const DrawQuad* quad) {
   DCHECK_EQ(quad->material, DrawQuad::SURFACE_CONTENT);
   return static_cast<const SurfaceDrawQuad*>(quad);
 }
 
 void SurfaceDrawQuad::ExtendValue(base::trace_event::TracedValue* value) const {
-  value->SetInteger("surface_id", surface_id.id);
+  value->SetString("surface_id", surface_id.ToString());
 }
 
 
 }  // namespace cc