[exp] cc: Introduce cc::CompositorMutator.

cc/trees/layer_tree_host_common.h

Index: cc/trees/layer_tree_host_common.h
diff --git a/cc/trees/layer_tree_host_common.h b/cc/trees/layer_tree_host_common.h
index 88197da329b7dc34dc2644aea5959a8545a83891..387138c163f100099668d7823820b2d4b0d930ad 100644
--- a/cc/trees/layer_tree_host_common.h
+++ b/cc/trees/layer_tree_host_common.h
@@ -23,6 +23,40 @@ class LayerImpl;
 class Layer;
 class SwapPromise;
 
+enum class MutationProperty {
+  MUTATION_PROPERTY_TRANSFORM = 1,
+  MUTATION_PROPERTY_OPACITY,
+};
+
+union MutationValue {
+  struct {
+    int old_value;
+    int new_value;
+  } i;
+
+  struct {
+    float old_value;
+    float new_value;
+  } f;
+};
+
+struct Mutation {
+  Mutation();
+  ~Mutation();
+
+  int proxy_id;
+  int mutated_properties;

[loyso (OOO), 2015/03/20 02:38:14]

Could you elaborate how we refer/identify properties?
How we apply updates? Thanks in advance!

+  std::vector<MutationValue> mutated_values;
+};
+
+class CompositorMutator {
+ public:
+  virtual ~CompositorMutator() {}
+
+  virtual void ApplyCustomMutations(base::TimeTicks monotonic_time,
+                                    const std::vector<Mutation>& mutations) = 0;
+};
+
 class CC_EXPORT LayerTreeHostCommon {
  public:
   static gfx::Rect CalculateVisibleRect(const gfx::Rect& target_surface_rect,