Add a cache of LayerImpl's viewport layer type

cc/trees/layer_tree_impl_unittest.cc

 // Copyright 2014 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_impl.h"
 
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "cc/layers/heads_up_display_layer_impl.h"
 #include "cc/test/fake_layer_tree_host_impl.h"
@@ skipping 2040 matching lines @@
   }
 
   host_impl().active_tree()->BuildPropertyTreesForTesting();
 
   float device_scale_factor = 3.f;
   float page_scale_factor = 5.f;
   gfx::Size scaled_bounds_for_root = gfx::ScaleToCeiledSize(
       root->bounds(), device_scale_factor * page_scale_factor);
   host_impl().SetViewportSize(scaled_bounds_for_root);
 
-  host_impl().active_tree()->SetViewportLayersFromIds(Layer::INVALID_ID, 1, 1,
-                                                      Layer::INVALID_ID);
+  host_impl().active_tree()->SetViewportLayersFromIds(
+      Layer::INVALID_ID, root->id(), Layer::INVALID_ID, Layer::INVALID_ID);
   host_impl().active_tree()->SetDeviceScaleFactor(device_scale_factor);
   host_impl().active_tree()->SetPageScaleOnActiveTree(page_scale_factor);
 
   host_impl().active_tree()->PushPageScaleFromMainThread(
       page_scale_factor, page_scale_factor, page_scale_factor);
   host_impl().active_tree()->SetPageScaleOnActiveTree(page_scale_factor);
   host_impl().UpdateNumChildrenAndDrawPropertiesForActiveTree();
 
   // Sanity check the scenario we just created.
   ASSERT_EQ(1u, GetRenderSurfaceList().size());
@@ skipping 277 matching lines @@
     auto weak_promise = promise->AsWeakPtr();
     host_impl().active_tree()->QueueSwapPromise(std::move(promise));
     host_impl().active_tree()->BreakSwapPromises(
         SwapPromise::DidNotSwapReason::SWAP_FAILS);
     EXPECT_FALSE(weak_promise);
   }
 }
 
 }  // namespace
 }  // namespace cc