VM: Fix race between background compiler and guarded cid update.

runtime/vm/weak_code.cc

 // Copyright (c) 2014, 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.
 
 #include "vm/weak_code.h"
 
 #include "platform/assert.h"
 
 #include "vm/code_generator.h"
 #include "vm/code_patcher.h"
@@ skipping 43 matching lines @@
     weak_property ^= dependent_code.At(i);
     if (code.raw() == weak_property.key()) {
       return true;
     }
   }
   return false;
 }
 
 
 void WeakCodeReferences::DisableCode() {
-  IncrementInvalidationGen();
   const Array& code_objects = Array::Handle(array_.raw());
   if (code_objects.IsNull()) {
     return;
   }
   ASSERT(!FLAG_precompiled_runtime);
   UpdateArrayTo(Object::null_array());
   // Disable all code on stack.
   Code& code = Code::Handle();
   {
     DartFrameIterator iterator;
@@ skipping 52 matching lines @@
       // Make non-OSR code non-entrant.
       if (!code.IsDisabled()) {
         ReportSwitchingCode(code);
         code.DisableDartCode();
       }
     }
   }
 }
 
 }  // namespace dart