base: Add missing "virtual" keyword and OVERRIDE to some methods.

base/json/json_parser.cc

Index: base/json/json_parser.cc
diff --git a/base/json/json_parser.cc b/base/json/json_parser.cc
index 738da473272273344c248a8c9baf52fe38d9baee..0cb59ee4947e42da3e5c60f7a85c08b21ddbf17b 100644
--- a/base/json/json_parser.cc
+++ b/base/json/json_parser.cc
@@ -140,12 +140,12 @@ class JSONStringValue : public base::Value {
         string_piece_(piece) {
   }
 
-  // Value:
-  bool GetAsString(std::string* out_value) const OVERRIDE {
+  // Overridden from base::Value:
+  virtual bool GetAsString(std::string* out_value) const OVERRIDE {
     string_piece_.CopyToString(out_value);
     return true;
   }
-  bool GetAsString(string16* out_value) const OVERRIDE {
+  virtual bool GetAsString(string16* out_value) const OVERRIDE {
     *out_value = UTF8ToUTF16(string_piece_);
     return true;
   }