Ensure the viewport is always represented by the inner viewport layer.

cc/trees/layer_tree_host_unittest.cc

 // Copyright 2011 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/trees/layer_tree_host.h"
 
 #include <algorithm>
 
 #include "base/auto_reset.h"
 #include "base/location.h"
@@ skipping 4990 matching lines @@
     recording->SetPlaybackAllowedEvent(&playback_allowed_event_);
     scoped_refptr<FakePictureLayer> layer =
         FakePictureLayer::CreateWithRecordingSource(layer_settings(), &client_,
                                                     recording.Pass());
     layer->SetBounds(gfx::Size(500, 500));
     layer->SetContentsOpaque(true);
     // Avoid LCD text on the layer so we don't cause extra commits when we
     // pinch.
     pinch->AddChild(layer);
 
-    layer_tree_host()->RegisterViewportLayers(NULL, root, pinch, pinch);
+    layer_tree_host()->RegisterViewportLayers(NULL, root, pinch, nullptr);
     layer_tree_host()->SetPageScaleFactorAndLimits(1.f, 1.f, 4.f);
     layer_tree_host()->SetRootLayer(root);
     LayerTreeHostTest::SetupTree();
   }
 
   // Returns the delta scale of all quads in the frame's root pass from their
   // ideal, or 0 if they are not all the same.
   float FrameQuadScaleDeltaFromIdeal(LayerTreeHostImpl::FrameData* frame_data) {
     if (frame_data->has_no_damage)
       return 0.f;
@@ skipping 278 matching lines @@
     recording->SetPlaybackAllowedEvent(&playback_allowed_event_);
     scoped_refptr<FakePictureLayer> layer =
         FakePictureLayer::CreateWithRecordingSource(layer_settings(), &client_,
                                                     recording.Pass());
     layer->SetBounds(gfx::Size(500, 500));
     layer->SetContentsOpaque(true);
     // Avoid LCD text on the layer so we don't cause extra commits when we
     // pinch.
     pinch->AddChild(layer);
 
-    layer_tree_host()->RegisterViewportLayers(NULL, root, pinch, pinch);
+    layer_tree_host()->RegisterViewportLayers(NULL, root, pinch, nullptr);
     layer_tree_host()->SetPageScaleFactorAndLimits(1.f, 1.f, 4.f);
     layer_tree_host()->SetRootLayer(root);
     LayerTreeHostTest::SetupTree();
   }
 
   // Returns the delta scale of all quads in the frame's root pass from their
   // ideal, or 0 if they are not all the same.
   float FrameQuadScaleDeltaFromIdeal(LayerTreeHostImpl::FrameData* frame_data) {
     if (frame_data->has_no_damage)
       return 0.f;
@@ skipping 1010 matching lines @@
     EndTest();
   }
 
   void AfterTest() override {}
 };
 
 MULTI_THREAD_TEST_F(LayerTreeHostTestDestroyWhileInitializingOutputSurface);
 
 }  // namespace
 }  // namespace cc