Update filter blending to match spec draft.

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 <cmath>
 
 #include "cc/output/filter_operations.h"
 
 #include "base/values.h"
 #include "cc/output/filter_operation.h"
@@ skipping 136 matching lines @@
 bool FilterOperations::HasReferenceFilter() const {
   for (size_t i = 0; i < operations_.size(); ++i) {
     if (operations_[i].type() == FilterOperation::REFERENCE)
       return true;
   }
   return false;
 }
 
 FilterOperations FilterOperations::Blend(const FilterOperations& from,
                                          double progress) const {
-  FilterOperations blended_filters;
-  if (from.size() == 0) {
-    for (size_t i = 0; i < size(); i++)
-      blended_filters.Append(FilterOperation::Blend(NULL, &at(i), progress));
-    return blended_filters;
+  if (HasReferenceFilter() || from.HasReferenceFilter())
+    return *this;
+
+  bool from_is_longer = from.size() > size();
+
+  size_t shorter_size, longer_size;
+  if (size() == from.size()) {
+    shorter_size = longer_size = size();
+  } else if  (from_is_longer) {
+    longer_size = from.size();
+    shorter_size = size();
+  } else {
+    longer_size = size();
+    shorter_size = from.size();
   }
 
-  if (size() == 0) {
-    for (size_t i = 0; i < from.size(); i++) {
-      blended_filters.Append(
-          FilterOperation::Blend(&from.at(i), NULL, progress));
-    }
-    return blended_filters;
-  }
-
-  if (from.size() != size())
-    return *this;
-
-  for (size_t i = 0; i < size(); i++) {
+  for (size_t i = 0; i < shorter_size; i++) {
     if (from.at(i).type() != at(i).type())
       return *this;
   }
 
-  for (size_t i = 0; i < size(); i++) {
+  FilterOperations blended_filters;
+  for (size_t i = 0; i < shorter_size; i++) {
     blended_filters.Append(
         FilterOperation::Blend(&from.at(i), &at(i), progress));
   }
 
+  if (from_is_longer) {
+    for (size_t i = shorter_size; i < longer_size; i++) {
+      blended_filters.Append(
+          FilterOperation::Blend(&from.at(i), NULL, progress));
+    }
+  } else {
+    for (size_t i = shorter_size; i < longer_size; i++)
+      blended_filters.Append(FilterOperation::Blend(NULL, &at(i), progress));
+  }
+
   return blended_filters;
 }
 
 scoped_ptr<base::Value> FilterOperations::AsValue() const {
   scoped_ptr<base::ListValue> value(new ListValue);
   for (size_t i = 0; i < operations_.size(); ++i)
     value->Append(operations_[i].AsValue().release());
   return value.PassAs<base::Value>();
 }
 
 }  // namespace cc