Add support for dumping code in jitdump file format

runtime/vm/code_observers.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_CODE_OBSERVERS_H_
 #define VM_CODE_OBSERVERS_H_
 
 #include "vm/globals.h"
 #include "vm/allocation.h"
 
 namespace dart {
 
+class Mutex;
+
 // Object observing code creation events. Used by external profilers and
 // debuggers to map address ranges to function names.
 class CodeObserver {
  public:
   CodeObserver() { }
 
   virtual ~CodeObserver() { }
 
   // Returns true if this observer is active and should be notified
   // about newly created code objects.
@@ skipping 23 matching lines @@
                         uword base,
                         uword prologue_offset,
                         uword size,
                         bool optimized);
 
   // Returns true if there is at least one active code observer.
   static bool AreActive();
 
   static void DeleteAll();
 
+  static Mutex* mutex() {
+    return mutex_;
+  }
+
  private:
+  static Mutex* mutex_;
   static intptr_t observers_length_;
   static CodeObserver** observers_;
 };
 
 
 }  // namespace dart
 
 #endif  // VM_CODE_OBSERVERS_H_