Refactor RegisterViewportLayers to use a struct instead of 6 values

cc/trees/layer_tree_host_unittest_scroll.cc

 // Copyright 2012 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 "base/location.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/weak_ptr.h"
 #include "base/single_thread_task_runner.h"
@@ skipping 1399 matching lines @@
       case 1:
         EndTest();
         break;
     }
   }
 
   void AfterTest() override {}
 
   virtual void DidScroll(Layer* layer) {
     if (scroll_destroy_whole_tree_) {
-      layer_tree_host()->RegisterViewportLayers(NULL, NULL, NULL, NULL, NULL,
-                                                NULL);
+      layer_tree_host()->RegisterViewportLayers(
+          LayerTreeHost::ViewportLayers());
       layer_tree_host()->SetRootLayer(NULL);
       EndTest();
       return;
     }
     layer->RemoveFromParent();
   }
 
  protected:
   class FakeLayerScrollClient {
    public:
@@ skipping 829 matching lines @@
   CompletionEvent* impl_side_invalidation_event_ = nullptr;
 
   // Main thread.
   int num_of_deltas_ = 0;
 };
 
 MULTI_THREAD_TEST_F(LayerTreeHostScrollTestImplSideInvalidation);
 
 }  // namespace
 }  // namespace cc