Fix GC problem with vm_handles in thread

runtime/vm/thread.h

 // Copyright (c) 2015, 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_THREAD_H_
 #define VM_THREAD_H_
 
 #include "vm/globals.h"
 #include "vm/handles.h"
 #include "vm/os_thread.h"
@@ skipping 330 matching lines @@
 #define REUSABLE_HANDLE_SCOPE_ACCESSORS(object)                                \
   void set_reusable_##object##_handle_scope_active(bool value) {               \
     reusable_##object##_handle_scope_active_ = value;                          \
   }                                                                            \
   bool reusable_##object##_handle_scope_active() const {                       \
     return reusable_##object##_handle_scope_active_;                           \
   }
   REUSABLE_HANDLE_LIST(REUSABLE_HANDLE_SCOPE_ACCESSORS)
 #undef REUSABLE_HANDLE_SCOPE_ACCESSORS
 
-bool IsAnyReusableHandleScopeActive() const {
+  bool IsAnyReusableHandleScopeActive() const {
 #define IS_REUSABLE_HANDLE_SCOPE_ACTIVE(object)                                \
-  if (reusable_##object##_handle_scope_active_) return true;
-  REUSABLE_HANDLE_LIST(IS_REUSABLE_HANDLE_SCOPE_ACTIVE)
-  return false;
+    if (reusable_##object##_handle_scope_active_) return true;
+    REUSABLE_HANDLE_LIST(IS_REUSABLE_HANDLE_SCOPE_ACTIVE)
+    return false;
 #undef IS_REUSABLE_HANDLE_SCOPE_ACTIVE
-}
+  }
 #endif  // defined(DEBUG)
 
+  void ClearReusableHandles();
+
 #define REUSABLE_HANDLE(object)                                                \
   object& object##Handle() const {                                             \
     return *object##_handle_;                                                  \
   }
   REUSABLE_HANDLE_LIST(REUSABLE_HANDLE)
 #undef REUSABLE_HANDLE
 
   void VisitObjectPointers(ObjectPointerVisitor* visitor);
 
  private:
@@ skipping 74 matching lines @@
   friend class ApiZone;
   friend class Isolate;
   friend class StackZone;
   friend class ThreadRegistry;
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 }  // namespace dart
 
 #endif  // VM_THREAD_H_