Add an ostream operator to Value (based on JSONWriter) so that assertions

base/values.h

Index: base/values.h
diff --git a/base/values.h b/base/values.h
index 83d046c7fea9530999b9d00fa3d1f2edcf44ec24..02a3566ec9cbf1949f122c9a8799efb3f83160e2 100644
--- a/base/values.h
+++ b/base/values.h
@@ -505,6 +505,9 @@ class BASE_EXPORT ValueSerializer {
   virtual Value* Deserialize(int* error_code, std::string* error_str) = 0;
 };
 
+// Stream operator so Values can be used in assertion statements.
+BASE_EXPORT std::ostream& operator<<(std::ostream& out, const Value& value);
+
 }  // namespace base
 
 // http://crbug.com/88666