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

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 205 matching lines @@
   }
 
   const uint8_t* CurrentBufferAddress() const {
     return stream_.AddressOfCurrentPosition();
   }
 
   void Advance(intptr_t value) {
     stream_.Advance(value);
   }
 
+  intptr_t PendingBytes() const {
+    return stream_.PendingBytes();
+  }
+
   RawSmi* ReadAsSmi();
   intptr_t ReadSmiValue();
 
   // Negative header value indicates VM isolate object id.
   bool IsVMIsolateObject(intptr_t header_value) { return (header_value < 0); }
   intptr_t GetVMIsolateObjectId(intptr_t header_val) {
     ASSERT(IsVMIsolateObject(header_val));
     intptr_t value = -header_val;  // Header is negative for VM isolate objects.
     ASSERT(SerializedHeaderTag::decode(value) == kObjectId);
     return SerializedHeaderData::decode(value);
@@ skipping 34 matching lines @@
 
   // Get an object from the backward references list.
   Object* GetBackRef(intptr_t id);
 
   // Read a full snap shot.
   RawApiError* ReadFullSnapshot();
 
   // Read a script snap shot.
   RawObject* ReadScriptSnapshot();
 
+  // Read version number of snapshot and verify.
+  RawApiError* VerifyVersion();
+
   // Helper functions for creating uninitialized versions
   // of various object types. These are used when reading a
   // full snapshot.
   RawArray* NewArray(intptr_t len);
   RawImmutableArray* NewImmutableArray(intptr_t len);
   RawOneByteString* NewOneByteString(intptr_t len);
   RawTwoByteString* NewTwoByteString(intptr_t len);
   RawTypeArguments* NewTypeArguments(intptr_t len);
   RawTokenStream* NewTokenStream(intptr_t len);
   RawContext* NewContext(intptr_t num_variables);
@@ skipping 297 matching lines @@
   }
   void set_exception_type(Exceptions::ExceptionType type) {
     exception_type_ = type;
   }
   const char* exception_msg() const { return exception_msg_; }
   void set_exception_msg(const char* msg) {
     exception_msg_ = msg;
   }
   void ThrowException(Exceptions::ExceptionType type, const char* msg);
 
+  // Write a version string for the snapshot.
+  void WriteVersion();
+
  protected:
   void UnmarkAll() {
     forward_list_.UnmarkAll();
   }
 
   bool CheckAndWritePredefinedObject(RawObject* raw);
   void HandleVMIsolateObject(RawObject* raw);
 
   void WriteObjectRef(RawObject* raw);
   void WriteClassId(RawClass* cls);
@@ skipping 118 matching lines @@
  private:
   SnapshotWriter* writer_;
   bool as_references_;
 
   DISALLOW_COPY_AND_ASSIGN(SnapshotWriterVisitor);
 };
 
 }  // namespace dart
 
 #endif  // VM_SNAPSHOT_H_