Make ContentDecryptionModuleResult cross-thread destructible.

Source/platform/ContentDecryptionModuleResult.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ContentDecryptionModuleResult_h
 #define ContentDecryptionModuleResult_h
 
 #include "platform/heap/Handle.h"
 #include "public/platform/WebContentDecryptionModuleException.h"
 #include "public/platform/WebContentDecryptionModuleResult.h"
@@ skipping 11 matching lines @@
     virtual void complete() = 0;
     virtual void completeWithContentDecryptionModule(WebContentDecryptionModule*) = 0;
     virtual void completeWithSession(WebContentDecryptionModuleResult::SessionStatus) = 0;
     virtual void completeWithError(WebContentDecryptionModuleException, unsigned long systemCode, const WebString&) = 0;
 
     WebContentDecryptionModuleResult result()
     {
         return WebContentDecryptionModuleResult(this);
     }
 
+    // WebContentDecryptionModuleResult may be destructed on a thread other
+    // than the Blink Oilpan thread that created it. To support that, mark
+    // it as cross-thread accessible (for WebContentDecryptionModuleResult's
+    // WebPrivatePtr<> to make use of.)
+    CROSS_THREAD_ACCESSIBLE();
     DEFINE_INLINE_VIRTUAL_TRACE() { }
 };
 
 } // namespace blink
 
 #endif // ContentDecryptionModuleResult_h