Store entry id as 32-bit int.

src/profile-generator.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 526 matching lines @@
             const char* name,
             SnapshotObjectId id,
             int self_size,
             int children_count,
             int retainers_count);
 
   HeapSnapshot* snapshot() { return snapshot_; }
   Type type() { return static_cast<Type>(type_); }
   const char* name() { return name_; }
   void set_name(const char* name) { name_ = name; }
-  inline SnapshotObjectId id();
+  inline SnapshotObjectId id() { return id_; }
   int self_size() { return self_size_; }
   int retained_size() { return retained_size_; }
   void add_retained_size(int size) { retained_size_ += size; }
   void set_retained_size(int value) { retained_size_ = value; }
   int ordered_index() { return ordered_index_; }
   void set_ordered_index(int value) { ordered_index_ = value; }
 
   Vector<HeapGraphEdge> children() {
     return Vector<HeapGraphEdge>(children_arr(), children_count_); }
   Vector<HeapGraphEdge*> retainers() {
@@ skipping 43 matching lines @@
 
   unsigned painted_: 1;
   unsigned type_: 4;
   int children_count_: 27;
   int retainers_count_;
   int self_size_;
   union {
     int ordered_index_;  // Used during dominator tree building.
     int retained_size_;  // At that moment, there is no retained size yet.
   };
+  SnapshotObjectId id_;
   HeapEntry* dominator_;
   HeapSnapshot* snapshot_;
-  struct Id {
-    uint32_t id1_;
-    uint32_t id2_;
-  } id_;  // This is to avoid extra padding of 64-bit value.
   const char* name_;
 
   DISALLOW_COPY_AND_ASSIGN(HeapEntry);
 };
 
 
 class HeapSnapshotsCollection;
 
 // HeapSnapshot represents a single heap snapshot. It is stored in
 // HeapSnapshotsCollection, which is also a factory for
@@ skipping 532 matching lines @@
 
   friend class HeapSnapshotJSONSerializerEnumerator;
   friend class HeapSnapshotJSONSerializerIterator;
 
   DISALLOW_COPY_AND_ASSIGN(HeapSnapshotJSONSerializer);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_PROFILE_GENERATOR_H_