Update filter blending to match spec draft.

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 410a50d937605ac6ae1b2dbcfc1c836e488ac986..66f586573ba19049a36ff476d382134d9683143b 100644
--- a/cc/output/filter_operations.h
+++ b/cc/output/filter_operations.h
@@ -56,18 +56,18 @@ class CC_EXPORT FilterOperations {
   }
 
   // If |from| is of the same size as this, where in each position, the filter
-  // in |from| is of the same type as the filter in this, returns a
-  // FilterOperations formed by linearly interpolating at each position a
-  // |progress| fraction of the way from the filter in |from|
-  // to the filter in this. If either |from| or this is an empty sequence,
-  // it is treated as a sequence of the same length as the other sequence,
-  // where the filter at each position is a no-op filter of the same type
-  // as the filter in that position in the other sequence. Otherwise, if
-  // both |from| and this are non-empty sequences but are either of different
-  // lengths or if there is a type mismatch at some position, returns a copy
-  // of this.
+  // in |from| is of the same type as the filter in this, and if this doesn't
+  // contain any reference filters, returns a FilterOperations formed by
+  // linearly interpolating at each position a |progress| fraction of the way
+  // from the filter in |from| to the filter in this. If |from| and this are of
+  // different lengths, they are treated as having the same length by padding
+  // the shorter sequence with no-op filters of the same type as the filters in
+  // the corresponding positions in the longer sequence. If either sequence has
+  // a reference filter or if there is a type mismatch at some position, returns
+  // a copy of this.
   FilterOperations Blend(const FilterOperations& from, double progress) const;
 
+
   scoped_ptr<base::Value> AsValue() const;
 
  private: