Add toString() for paint property node classes

cc/output/filter_operations.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/output/filter_operations.h"
 
 #include <stddef.h>
 
 #include <cmath>
 #include <numeric>
@@ skipping 227 matching lines @@
 
 void FilterOperations::AsValueInto(
     base::trace_event::TracedValue* value) const {
   for (size_t i = 0; i < operations_.size(); ++i) {
     value->BeginDictionary();
     operations_[i].AsValueInto(value);
     value->EndDictionary();
   }
 }
 
+std::string FilterOperations::ToString() const {
+  base::trace_event::TracedValue value;
+  value.BeginArray("FilterOperations");
+  AsValueInto(&value);
+  value.EndArray();
+  return value.ToString();
+}
+
 }  // namespace cc