cc: Partial tile update for one-copy raster.

cc/resources/resource_provider.h

Index: cc/resources/resource_provider.h
diff --git a/cc/resources/resource_provider.h b/cc/resources/resource_provider.h
index f7baac1e3bb1447b60b10bee6aef281a7904a778..974de3c2113ef2230b03049c146409b60c3e1cb2 100644
--- a/cc/resources/resource_provider.h
+++ b/cc/resources/resource_provider.h
@@ -333,6 +333,23 @@ class CC_EXPORT ResourceProvider {
     DISALLOW_COPY_AND_ASSIGN(ScopedWriteLockGpuMemoryBuffer);
   };
 
+  class CC_EXPORT ScopedReadLockGpuMemoryBuffer {
+   public:
+    ScopedReadLockGpuMemoryBuffer(ResourceProvider* resource_provider,
+                                  ResourceProvider::ResourceId resource_id);
+    ~ScopedReadLockGpuMemoryBuffer();
+
+    gfx::GpuMemoryBuffer* GetGpuMemoryBuffer();
+
+   private:
+    ResourceProvider* resource_provider_;
+    ResourceProvider::ResourceId resource_id_;
+    gfx::GpuMemoryBuffer* gpu_memory_buffer_;
+    base::ThreadChecker thread_checker_;
+
+    DISALLOW_COPY_AND_ASSIGN(ScopedReadLockGpuMemoryBuffer);
+  };
+
   class CC_EXPORT ScopedWriteLockGr {
    public:
     ScopedWriteLockGr(ResourceProvider* resource_provider,