cc: Implement and use FilterOperations::MapRectReverse for mapping backdrop bounding box.

cc/output/filter_operations.h

Index: cc/output/filter_operations.h
diff --git a/cc/output/filter_operations.h b/cc/output/filter_operations.h
index 589b2f5f5bb107206fd809b7be1815f4b7b7c127..d07854d74456ea76dc2034c73a401f44968d88ed 100644
--- a/cc/output/filter_operations.h
+++ b/cc/output/filter_operations.h
@@ -54,6 +54,10 @@ class CC_EXPORT FilterOperations {
   // by pixels in the source rect.
   gfx::Rect MapRect(const gfx::Rect& rect, const SkMatrix& matrix) const;
 
+  // Maps "backward" to determine which pixels in the source affect the pixels
+  // in the destination rect.
+  gfx::Rect MapRectReverse(const gfx::Rect& rect, const SkMatrix& matrix) const;
+
   void GetOutsets(int* top, int* right, int* bottom, int* left) const;
   bool HasFilterThatMovesPixels() const;
   bool HasFilterThatAffectsOpacity() const;