Fix cc scrollbar layer issues with initialization, and use element ids throughout.

third_party/WebKit/Source/platform/graphics/CompositorMutableStateProvider.cpp

 // Copyright 2016 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 "platform/graphics/CompositorMutableStateProvider.h"
 
 #include <memory>
 #include "cc/layers/layer_impl.h"
 #include "cc/trees/layer_tree_impl.h"
 #include "platform/graphics/CompositorElementId.h"
 #include "platform/graphics/CompositorMutableProperties.h"
 #include "platform/graphics/CompositorMutableState.h"
 #include "platform/graphics/CompositorMutation.h"
 #include "platform/wtf/PtrUtil.h"
 
 namespace blink {
 
 CompositorMutableStateProvider::CompositorMutableStateProvider(
     cc::LayerTreeImpl* tree_impl,
     CompositorMutations* mutations)
     : tree_(tree_impl), mutations_(mutations) {}
 
 CompositorMutableStateProvider::~CompositorMutableStateProvider() {}
 
 std::unique_ptr<CompositorMutableState>
 CompositorMutableStateProvider::GetMutableStateFor(uint64_t element_id) {
-  cc::LayerImpl* main_layer = tree_->LayerByElementId(
-      CreateCompositorElementId(element_id, CompositorSubElementId::kPrimary));
-  cc::LayerImpl* scroll_layer = tree_->LayerByElementId(
-      CreateCompositorElementId(element_id, CompositorSubElementId::kScroll));
+  cc::LayerImpl* main_layer =
+      tree_->LayerByElementId(CompositorElementIdFromDOMNodeId(
+          element_id, CompositorElementIdNamespace::kPrimary));
+  cc::LayerImpl* scroll_layer =
+      tree_->LayerByElementId(CompositorElementIdFromDOMNodeId(
+          element_id, CompositorElementIdNamespace::kScroll));
 
   if (!main_layer && !scroll_layer)
     return nullptr;
 
   // Ensure that we have an entry in the map for |elementId| but do as few
   // allocations and queries as possible. This will update the map only if we
   // have not added a value for |elementId|.
   auto result = mutations_->map.insert(element_id, nullptr);
 
   // Only if this is a new entry do we want to allocate a new mutation.
   if (result.is_new_entry)
     result.stored_value->value = WTF::WrapUnique(new CompositorMutation);
 
   return WTF::WrapUnique(new CompositorMutableState(
       result.stored_value->value.get(), main_layer, scroll_layer));
 }
 
 }  // namespace blink