Change snapshot versioning code to use plain strings instead of Dart strings

runtime/vm/datastream.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_DATASTREAM_H_
 #define VM_DATASTREAM_H_
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/allocation.h"
@@ skipping 80 matching lines @@
 
   const uint8_t* AddressOfCurrentPosition() const {
     return current_;
   }
 
   void Advance(intptr_t value) {
     ASSERT((end_ - current_) > value);
     current_ = current_ + value;
   }
 
+  intptr_t PendingBytes() const {
+    ASSERT(end_ >= current_);
+    return (end_ - current_);
+  }
+
  private:
   template<typename T>
   T Read() {
     return Read<T>(kEndByteMarker);
   }
 
   int16_t Read16() {
     return Read16(kEndByteMarker);
   }
 
@@ skipping 317 matching lines @@
   intptr_t current_size_;
   ReAlloc alloc_;
   intptr_t initial_size_;
 
   DISALLOW_COPY_AND_ASSIGN(WriteStream);
 };
 
 }  // namespace dart
 
 #endif  // VM_DATASTREAM_H_