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

cc/trees/layer_tree_host_unittest_picture.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/trees/layer_tree_host.h"
 
 #include "cc/test/fake_content_layer_client.h"
 #include "cc/test/fake_picture_layer.h"
 #include "cc/test/fake_picture_layer_impl.h"
 #include "cc/test/layer_tree_test.h"
@@ skipping 392 matching lines @@
     pinch_->SetScrollClipLayerId(root->id());
     pinch_->SetIsContainerForFixedPositionLayers(true);
     root->AddChild(pinch_);
 
     // Don't be solid color so the layer has tilings/tiles.
     client_.set_fill_with_nonsolid_color(true);
     picture_ = FakePictureLayer::Create(layer_settings(), &client_);
     picture_->SetBounds(gfx::Size(100, 100));
     pinch_->AddChild(picture_);
 
-    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);
     LayerTreeHostPictureTest::SetupTree();
   }
 
   void InitializeSettings(LayerTreeSettings* settings) override {
     settings->layer_transforms_should_scale_layer_contents = true;
   }
 
   void BeginTest() override {
@@ skipping 130 matching lines @@
   int last_frame_drawn_;
   bool ready_to_draw_;
 };
 
 // Multi-thread only because in single thread you can't pinch zoom on the
 // compositor thread.
 MULTI_THREAD_TEST_F(LayerTreeHostPictureTestRSLLMembershipWithScale);
 
 }  // namespace
 }  // namespace cc