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 fae06f87f8a282ae07eb61f111a3c9e31e595543..d0d768acb281186da448d4b60e2c2ac92c950df6 100644
--- a/cc/output/filter_operation.h
+++ b/cc/output/filter_operation.h
@@ -23,6 +23,10 @@ class TracedValue;
 class Value;
 }
 
+namespace gfx {
+class Rect;
+}
+
 namespace cc {
 
 class CC_EXPORT FilterOperation {
@@ -226,6 +230,10 @@ 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);