Implement cc::FilterOperation StructTraits

cc/output/filter_operation.cc

Index: cc/output/filter_operation.cc
diff --git a/cc/output/filter_operation.cc b/cc/output/filter_operation.cc
index 78588748ba59d63c5d68bd35e1df56cba76f0d22..c98990fc6198950a7b6c8324f47ccfeba3d412a6 100644
--- a/cc/output/filter_operation.cc
+++ b/cc/output/filter_operation.cc
@@ -27,8 +27,9 @@ bool FilterOperation::operator==(const FilterOperation& other) const {
            drop_shadow_offset_ == other.drop_shadow_offset_ &&
            drop_shadow_color_ == other.drop_shadow_color_;
   }
-  if (type_ == REFERENCE)
+  if (type_ == REFERENCE) {
     return image_filter_.get() == other.image_filter_.get();
+  }
   if (type_ == ALPHA_THRESHOLD) {
     return region_ == other.region_ &&
         amount_ == other.amount_ &&
@@ -37,6 +38,8 @@ bool FilterOperation::operator==(const FilterOperation& other) const {
   return amount_ == other.amount_;
 }
 
+FilterOperation::FilterOperation() : FilterOperation(GRAYSCALE, 0.f) {}
+
 FilterOperation::FilterOperation(FilterType type, float amount)
     : type_(type),
       amount_(amount),