Fix UpdateTilePriorities viewport in Android WebView.

cc/test/pixel_test_output_surface.cc

 // Copyright 2013 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/test/pixel_test_output_surface.h"
 
 #include "cc/output/output_surface_client.h"
 #include "ui/gfx/transform.h"
 
 namespace cc {
 
 void PixelTestOutputSurface::Reshape(gfx::Size size, float scale_factor) {
   gfx::Size expanded_size(size.width() + surface_expansion_size_.width(),
                           size.height() + surface_expansion_size_.height());
   OutputSurface::Reshape(expanded_size, scale_factor);
 
   gfx::Rect offset_viewport = gfx::Rect(size) + viewport_offset_;
-  SetExternalDrawConstraints(gfx::Transform(), offset_viewport);
+  gfx::Rect offset_clip = device_clip_.IsEmpty()
+                              ? offset_viewport
+                              : device_clip_ + viewport_offset_;
+  SetExternalDrawConstraints(
+      gfx::Transform(), offset_viewport, offset_clip, true);
 }
 
 }  // namespace cc