Do not invoke async method on a GC-unreachable object.

Source/platform/AsyncMethodRunner.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 102 matching lines @@
         if (m_timer.isActive())
             m_timer.stop();
     }
 
     bool isActive() const
     {
         return m_timer.isActive();
     }
 
 private:
-    void fired(Timer<AsyncMethodRunner<TargetClass>>*) { (m_object->*m_method)(); }
+    void fired(Timer<AsyncMethodRunner<TargetClass>>*)
+    {
+        // TODO(Oilpan): when AsyncMethodRunner is on the heap, this check becomes
+        // redundant; handled directly by Timer<> instead.
+        if (!TimerIsObjectAliveTrait<TargetClass>::isHeapObjectAlive(m_object))
+            return;
+        (m_object->*m_method)();
+    }
 
     Timer<AsyncMethodRunner<TargetClass>> m_timer;
 
-    // FIXME: oilpan: AsyncMethodRunner should be moved to the heap and m_object should be traced.
+    // TODO(Oilpan): AsyncMethodRunner should be moved to the heap and m_object should be traced.
     // This raw pointer is safe as long as AsyncMethodRunner<X> is held by the X itself
     // (That's the case in the current code base).
     GC_PLUGIN_IGNORE("363031")
     TargetClass* m_object;
     TargetMethod m_method;
 
     bool m_suspended;
     bool m_runWhenResumed;
 };
 
 }
 
 #endif