Expand the class id to 32 bits and size field to 16 bits on 64-bit platforms.

runtime/vm/snapshot.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_SNAPSHOT_H_
 #define VM_SNAPSHOT_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/bitfield.h"
@@ skipping 177 matching lines @@
   template <typename T>
   T Read() {
     return ReadStream::Raw<sizeof(T), T>::Read(&stream_);
   }
 
   intptr_t ReadRawPointerValue() {
     int64_t value = Read<int64_t>();
     return static_cast<intptr_t>(value);
   }
 
+  classid_t ReadClassIDValue() {
+    uint32_t value = Read<uint32_t>();
+    return static_cast<classid_t>(value);
+  }
+  COMPILE_ASSERT(sizeof(uint32_t) >= sizeof(classid_t));
+
   void ReadBytes(uint8_t* addr, intptr_t len) {
     stream_.ReadBytes(addr, len);
   }
 
   double ReadDouble() {
     double result;
     stream_.ReadBytes(reinterpret_cast<uint8_t*>(&result), sizeof(result));
     return result;
   }
 
@@ skipping 296 matching lines @@
   // sizeof(T) must be in {1,2,4,8}.
   template <typename T>
   void Write(T value) {
     WriteStream::Raw<sizeof(T), T>::Write(&stream_, value);
   }
 
   void WriteRawPointerValue(intptr_t value) {
     Write<int64_t>(value);
   }
 
+  void WriteClassIDValue(classid_t value) {
+    Write<uint32_t>(value);
+  }
+  COMPILE_ASSERT(sizeof(uint32_t) >= sizeof(classid_t));
+
   // Write an object that is serialized as an Id (singleton in object store,
   // or an object that was already serialized before).
   void WriteIndexedObject(intptr_t object_id) {
     ASSERT(object_id <= kMaxObjectId);
     intptr_t value = 0;
     value = SerializedHeaderTag::update(kObjectId, value);
     value = SerializedHeaderData::update(object_id, value);
     Write<int32_t>(value);
   }
 
@@ skipping 324 matching lines @@
  private:
   SnapshotWriter* writer_;
   bool as_references_;
 
   DISALLOW_COPY_AND_ASSIGN(SnapshotWriterVisitor);
 };
 
 }  // namespace dart
 
 #endif  // VM_SNAPSHOT_H_