Refactor SetViewportLayerIds to use a struct instead of 6 values

cc/layers/layer_impl_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/layers/layer_impl.h"
 
 #include "cc/base/filter_operation.h"
 #include "cc/base/filter_operations.h"
 #include "cc/layers/painted_scrollbar_layer_impl.h"
 #include "cc/layers/solid_color_scrollbar_layer_impl.h"
@@ skipping 122 matching lines @@
       LayerImpl::Create(host_impl.active_tree(), 1);
   LayerImpl* root_clip = root_clip_ptr.get();
   std::unique_ptr<LayerImpl> root_ptr =
       LayerImpl::Create(host_impl.active_tree(), 2);
   LayerImpl* root = root_ptr.get();
   root_clip_ptr->test_properties()->AddChild(std::move(root_ptr));
   host_impl.active_tree()->SetRootLayerForTesting(std::move(root_clip_ptr));
 
   // Make root the inner viewport scroll layer. This ensures the later call to
   // |SetViewportBoundsDelta| will be on a viewport layer.
-  host_impl.active_tree()->SetViewportLayersFromIds(
-      Layer::INVALID_ID, Layer::INVALID_ID, Layer::INVALID_ID,
-      Layer::INVALID_ID, root->id(), Layer::INVALID_ID);
+  LayerTreeImpl::ViewportLayerIds viewport_ids;
+  viewport_ids.inner_viewport_scroll = root->id();
+  host_impl.active_tree()->SetViewportLayersFromIds(viewport_ids);
 
   root->test_properties()->force_render_surface = true;
   root->SetMasksToBounds(true);
   root->layer_tree_impl()->ResetAllChangeTracking();
 
   root->test_properties()->AddChild(
       LayerImpl::Create(host_impl.active_tree(), 7));
   LayerImpl* child = root->test_properties()->children[0];
   child->test_properties()->AddChild(
       LayerImpl::Create(host_impl.active_tree(), 8));
@@ skipping 451 matching lines @@
 
   pending_layer->PushPropertiesTo(layer());
 
   EXPECT_VECTOR_EQ(gfx::Vector2dF(22, 23), layer()->CurrentScrollOffset());
   EXPECT_VECTOR_EQ(layer()->CurrentScrollOffset(),
                    pending_layer->CurrentScrollOffset());
 }
 
 }  // namespace
 }  // namespace cc