Refactor SetViewportLayerIds to use a struct instead of 6 values

cc/test/fake_layer_tree_host.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/fake_layer_tree_host.h"
 
 #include "base/memory/ptr_util.h"
 #include "base/single_thread_task_runner.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "cc/animation/animation_host.h"
@@ skipping 61 matching lines @@
   TreeSynchronizer::SynchronizeTrees(root_layer(), active_tree());
   active_tree()->SetPropertyTrees(property_trees());
   TreeSynchronizer::PushLayerProperties(root_layer()->layer_tree_host(),
                                         active_tree());
   mutator_host()->PushPropertiesTo(host_impl_.mutator_host());
 
   active_tree()->property_trees()->scroll_tree.PushScrollUpdatesFromMainThread(
       property_trees(), active_tree());
 
   if (page_scale_layer() && inner_viewport_scroll_layer()) {
-    active_tree()->SetViewportLayersFromIds(
-        overscroll_elasticity_layer() ? overscroll_elasticity_layer()->id()
-                                      : Layer::INVALID_ID,
-        page_scale_layer()->id(),
-        inner_viewport_container_layer()
-            ? inner_viewport_container_layer()->id()
-            : Layer::INVALID_ID,
-        outer_viewport_container_layer()
-            ? outer_viewport_container_layer()->id()
-            : Layer::INVALID_ID,
-        inner_viewport_scroll_layer()->id(),
-        outer_viewport_scroll_layer() ? outer_viewport_scroll_layer()->id()
-                                      : Layer::INVALID_ID);
+    LayerTreeImpl::ViewportLayerIds ids;
+    if (overscroll_elasticity_layer())
+      ids.overscroll_elasticity = overscroll_elasticity_layer()->id();
+    ids.page_scale = page_scale_layer()->id();
+    if (inner_viewport_container_layer())
+      ids.inner_viewport_container = inner_viewport_container_layer()->id();
+    if (outer_viewport_container_layer())
+      ids.outer_viewport_container = outer_viewport_container_layer()->id();
+    ids.inner_viewport_scroll = inner_viewport_scroll_layer()->id();
+    if (outer_viewport_scroll_layer())
+      ids.outer_viewport_scroll = outer_viewport_scroll_layer()->id();
+    active_tree()->SetViewportLayersFromIds(ids);
   }
 
   return active_tree()->root_layer_for_testing();
 }
 
 LayerImpl* FakeLayerTreeHost::CommitAndCreatePendingTree() {
   TreeSynchronizer::SynchronizeTrees(root_layer(), pending_tree());
   pending_tree()->SetPropertyTrees(property_trees());
   TreeSynchronizer::PushLayerProperties(root_layer()->layer_tree_host(),
                                         pending_tree());
   mutator_host()->PushPropertiesTo(host_impl_.mutator_host());
 
   pending_tree()->property_trees()->scroll_tree.PushScrollUpdatesFromMainThread(
       property_trees(), pending_tree());
   return pending_tree()->root_layer_for_testing();
 }
 
 }  // namespace cc