compositor-worker: Introduce WebCompositorMutableState

cc/blink/web_compositor_mutable_state_provider_impl.cc

Index: cc/blink/web_compositor_mutable_state_provider_impl.cc
diff --git a/cc/blink/web_compositor_mutable_state_provider_impl.cc b/cc/blink/web_compositor_mutable_state_provider_impl.cc
new file mode 100644
index 0000000000000000000000000000000000000000..713a5428a5d1aad3d1fee91efc0fbc7f759c1cde
--- /dev/null
+++ b/cc/blink/web_compositor_mutable_state_provider_impl.cc
@@ -0,0 +1,34 @@
+// 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/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::WebPassOwnPtr<blink::WebCompositorMutableState>
+WebCompositorMutableStateProviderImpl::getMutableStateFor(uint64_t element_id) {
+  cc::LayerTreeImpl::ElementLayers layers =
+      state_->GetMutableLayers(element_id);
+
+  if (!layers.main && !layers.scroll)
+    return nullptr;
+
+  return blink::adoptWebPtr<blink::WebCompositorMutableState>(
+      new WebCompositorMutableStateImpl(&(*mutations_)[element_id], layers.main,
+                                        layers.scroll));
+}
+
+}  // namespace cc_blink