Implement cc::FilterOperations::MapRect.

cc/output/filter_operation.h

Index: cc/output/filter_operation.h
diff --git a/cc/output/filter_operation.h b/cc/output/filter_operation.h
index 44590c233ba35792ef2bbaa7d2ca390b137cccc3..477759c660b8720f0761ee7d6cac65c93ffc6a94 100644
--- a/cc/output/filter_operation.h
+++ b/cc/output/filter_operation.h
@@ -22,6 +22,10 @@ class TracedValue;
 class Value;
 }
 
+namespace gfx {
+class Rect;
+}
+
 namespace cc {
 
 class CC_EXPORT FilterOperation {
@@ -225,6 +229,10 @@ class CC_EXPORT FilterOperation {
 
   void AsValueInto(base::trace_event::TracedValue* value) const;
 
+  // Maps "forward" to determine which pixels in a destination rect are affected
+  // by pixels in the source rect.
+  gfx::Rect MapRect(const gfx::Rect& rect) const;
+
  private:
   FilterOperation(FilterType type, float amount);