cc/blimp: Add a LayerTreeHostRemote implementation.

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index 5610ff703430ad2fd8e0630e05e8b64c01de46c8..64362044abe9bfbae5874c5c4c12c7f3038c1ddb 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -199,6 +199,10 @@ class CC_EXPORT LayerTreeHost {
   // The LayerTreeHost tracks whether the content is suitable for Gpu raster.
   // Calling this will reset it back to not suitable state.
   virtual void ResetGpuRasterizationTracking() = 0;
+
+ protected:
+  // Used to generate a unique identifier for a LayerTreeHost.
+  static int GenerateHostId();
 };
 
 }  // namespace cc