Eagerly sweep MediaKeySession objects.

Source/modules/encryptedmedia/MediaKeysController.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 MediaKeysController_h
 #define MediaKeysController_h
 
 #include "core/page/Page.h"
 #include "modules/ModulesExport.h"
-#include "wtf/PassOwnPtr.h"
 
 namespace blink {
 
 class ExecutionContext;
 class MediaKeysClient;
-class WebContentDecryptionModule;
 class WebEncryptedMediaClient;
 
 class MODULES_EXPORT MediaKeysController final : public NoBaseWillBeGarbageCollected<MediaKeysController>, public WillBeHeapSupplement<Page> {
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(MediaKeysController);
 public:
     WebEncryptedMediaClient* encryptedMediaClient(ExecutionContext*);
 
     static void provideMediaKeysTo(Page&, MediaKeysClient*);
     static MediaKeysController* from(Page* page) { return static_cast<MediaKeysController*>(WillBeHeapSupplement<Page>::from(page, supplementName())); }
 
     DEFINE_INLINE_VIRTUAL_TRACE() { WillBeHeapSupplement<Page>::trace(visitor); }
 
 private:
     explicit MediaKeysController(MediaKeysClient*);
     static const char* supplementName();
+
+    // Raw reference to the client implementation, which is currently owned
+    // by the WebView. Its lifetime extends past any m_client accesses.
+    // It is not on the Oilpan heap.
     MediaKeysClient* m_client;
 };
 
 } // namespace blink
 
 #endif // MediaKeysController_h