Add missing mutex protection for timeout queue with mutex

runtime/bin/eventhandler.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 BIN_EVENTHANDLER_H_
 #define BIN_EVENTHANDLER_H_
 
 #include "bin/builtin.h"
 #include "bin/isolate_data.h"
 
@@ skipping 47 matching lines @@
  public:
   TimeoutQueue() : next_timeout_(NULL), timeouts_(NULL) {}
 
   ~TimeoutQueue() {
     while (HasTimeout()) RemoveCurrent();
   }
 
   bool HasTimeout() const { return next_timeout_ != NULL; }
 
   int64_t CurrentTimeout() const {
+    ASSERT(next_timeout_ != NULL);
     return next_timeout_->timeout();
   }
 
   Dart_Port CurrentPort() const {
+    ASSERT(next_timeout_ != NULL);
     return next_timeout_->port();
   }
 
   void RemoveCurrent() {
     UpdateTimeout(CurrentPort(), -1);
   }
 
   void UpdateTimeout(Dart_Port port, int64_t timeout);
 
  private:
@@ skipping 41 matching lines @@
 
  private:
   friend class EventHandlerImplementation;
   EventHandlerImplementation delegate_;
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_EVENTHANDLER_H_