Fix uninitialized variable compiler errors [GCC 4.8.4]

src/runtime/runtime-classes.cc

Index: src/runtime/runtime-classes.cc
diff --git a/src/runtime/runtime-classes.cc b/src/runtime/runtime-classes.cc
index b4b1ba7773d1db862e48055dde679fdfc7619f00..51247b728cf60730d3089b4a5bce6472673172ab 100644
--- a/src/runtime/runtime-classes.cc
+++ b/src/runtime/runtime-classes.cc
@@ -306,7 +306,7 @@ RUNTIME_FUNCTION(Runtime_LoadKeyedFromSuper) {
   CONVERT_ARG_HANDLE_CHECKED(JSObject, home_object, 1);
   CONVERT_ARG_HANDLE_CHECKED(Object, key, 2);
 
-  uint32_t index;
+  uint32_t index = 0;
   if (key->ToArrayIndex(&index)) {
     return LoadElementFromSuper(isolate, receiver, home_object, index);
   }
@@ -394,7 +394,7 @@ static Object* StoreKeyedToSuper(Isolate* isolate, Handle<JSObject> home_object,
                                  Handle<Object> receiver, Handle<Object> key,
                                  Handle<Object> value,
                                  LanguageMode language_mode) {
-  uint32_t index;
+  uint32_t index = 0;
 
   if (key->ToArrayIndex(&index)) {
     return StoreElementToSuper(isolate, home_object, receiver, index, value,