Add a few missing overrides found by a new clang warning.

src/serialize.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_SERIALIZE_H_
 #define V8_SERIALIZE_H_
 
 #include "src/compiler.h"
 #include "src/hashmap.h"
 #include "src/heap-profiler.h"
@@ skipping 612 matching lines @@
                     Serializer* startup_snapshot_serializer,
                     SnapshotByteSink* sink)
     : Serializer(isolate, sink),
       startup_serializer_(startup_snapshot_serializer) {
     InitializeCodeAddressMap();
   }
 
   // Serialize the objects reachable from a single object pointer.
   void Serialize(Object** o);
   virtual void SerializeObject(HeapObject* o, HowToCode how_to_code,
-                               WhereToPoint where_to_point, int skip);
+                               WhereToPoint where_to_point, int skip) OVERRIDE;
 
  private:
   int PartialSnapshotCacheIndex(HeapObject* o);
   bool ShouldBeInThePartialSnapshotCache(HeapObject* o) {
     // Scripts should be referred only through shared function infos.  We can't
     // allow them to be part of the partial snapshot because they contain a
     // unique ID, and deserializing several partial snapshots containing script
     // would cause dupes.
     DCHECK(!o->IsScript());
     return o->IsName() || o->IsSharedFunctionInfo() ||
@@ skipping 24 matching lines @@
   // The StartupSerializer has to serialize the root array, which is slightly
   // different.
   virtual void VisitPointers(Object** start, Object** end) OVERRIDE;
 
   // Serialize the current state of the heap.  The order is:
   // 1) Strong references.
   // 2) Partial snapshot cache.
   // 3) Weak references (e.g. the string table).
   virtual void SerializeStrongReferences();
   virtual void SerializeObject(HeapObject* o, HowToCode how_to_code,
-                               WhereToPoint where_to_point, int skip);
+                               WhereToPoint where_to_point, int skip) OVERRIDE;
   void SerializeWeakReferences();
   void Serialize() {
     SerializeStrongReferences();
     SerializeWeakReferences();
     Pad();
   }
 
  private:
   intptr_t root_index_wave_front_;
   DISALLOW_COPY_AND_ASSIGN(StartupSerializer);
@@ skipping 24 matching lines @@
   CodeSerializer(Isolate* isolate, SnapshotByteSink* sink, String* source,
                  Code* main_code)
       : Serializer(isolate, sink),
         source_(source),
         main_code_(main_code),
         num_internalized_strings_(0) {
     back_reference_map_.AddSourceString(source);
   }
 
   virtual void SerializeObject(HeapObject* o, HowToCode how_to_code,
-                               WhereToPoint where_to_point, int skip);
+                               WhereToPoint where_to_point, int skip) OVERRIDE;
 
   void SerializeBuiltin(int builtin_index, HowToCode how_to_code,
                         WhereToPoint where_to_point);
   void SerializeIC(Code* ic, HowToCode how_to_code,
                    WhereToPoint where_to_point);
   void SerializeCodeStub(uint32_t stub_key, HowToCode how_to_code,
                          WhereToPoint where_to_point);
   void SerializeSourceObject(HowToCode how_to_code,
                              WhereToPoint where_to_point);
   void SerializeGeneric(HeapObject* heap_object, HowToCode how_to_code,
@@ skipping 110 matching lines @@
   // Following the header, we store, in sequential order
   // - code stub keys
   // - serialization payload
 
   ScriptData* script_data_;
   bool owns_script_data_;
 };
 } }  // namespace v8::internal
 
 #endif  // V8_SERIALIZE_H_