compositor-worker: Introduce WebCompositorMutableState

cc/blink/web_compositor_mutable_state_provider_impl.cc

+// Copyright 2015 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/blink/web_compositor_mutable_state_provider_impl.h"
+
+#include "cc/animation/layer_tree_mutation.h"
+#include "cc/blink/web_compositor_mutable_state_impl.h"
+#include "cc/layers/layer_impl.h"
+#include "cc/trees/layer_tree_impl.h"
+
+namespace cc_blink {
+
+WebCompositorMutableStateProviderImpl::WebCompositorMutableStateProviderImpl(
+    cc::LayerTreeImpl* state,
+    cc::LayerTreeMutationMap* mutations)
+    : state_(state), mutations_(mutations) {}
+
+WebCompositorMutableStateProviderImpl::
+    ~WebCompositorMutableStateProviderImpl() {}
+
+blink::WebCompositorMutableState*
+WebCompositorMutableStateProviderImpl::getMutableStateFor(uint64_t element_id) {
+  cc::LayerTreeImpl::ElementLayers layers =
+      state_->GetMutableLayers(element_id);
+
+  if (!layers.main && !layers.scroll)
+    return nullptr;
+
+  return new WebCompositorMutableStateImpl(&(*mutations_)[element_id],
+                                           layers.main, layers.scroll);
+}
+
+}  // namespace cc_blink