Added API Dart_PostCMessage for posting a Dart_CMessage structure

runtime/vm/snapshot.h

Index: runtime/vm/snapshot.h
diff --git a/runtime/vm/snapshot.h b/runtime/vm/snapshot.h
index 166ea06ee89e899b0714b4203faf0dee7705f29d..6b58dabb304d307c63d2886e15ae265cdbe3ea7a 100644
--- a/runtime/vm/snapshot.h
+++ b/runtime/vm/snapshot.h
@@ -531,18 +531,39 @@ class BaseWriter {
 
 class MessageWriter : public BaseWriter {
  public:
-  MessageWriter(uint8_t** buffer, ReAlloc alloc) : BaseWriter(buffer, alloc) {
+  MessageWriter(uint8_t** buffer, ReAlloc alloc)
+      : BaseWriter(buffer, alloc), object_id_(0) {
+    ASSERT(kDartCObjectTypeMask >= Dart_CObject::kNumberOfTypes);
   }
   ~MessageWriter() { }
 
   // Writes a message of integers.
   void WriteMessage(intptr_t field_count, intptr_t *data);
 
+  void WriteCMessage(Dart_CObject* object);
+
   void FinalizeBuffer() {
     BaseWriter::FinalizeBuffer(Snapshot::kMessage);
   }
 
  private:
+  static const intptr_t kDartCObjectTypeBits = 3;
+  static const intptr_t kDartCObjectTypeMask = (1 << kDartCObjectTypeBits) - 1;
+  static const intptr_t kDartCObjectMarkMask = ~kDartCObjectTypeMask;
+  static const intptr_t kDartCObjectMarkOffset = 1;
+
+  void MarkCObject(Dart_CObject* object, intptr_t object_id);
+  void UnmarkCObject(Dart_CObject* object);
+  bool IsCObjectMarked(Dart_CObject* object);
+  intptr_t GetMarkedCObjectMark(Dart_CObject* object);
+  void UnmarkAllCObjects(Dart_CObject* object);
+
+  void WriteSmi(int32_t value);
+  void WriteInlinedHeader(Dart_CObject* object);
+  void WriteCObject(Dart_CObject* object);
+
+  intptr_t object_id_;
+
   DISALLOW_COPY_AND_ASSIGN(MessageWriter);
 };