Set callback interface on WebCDMSession after creation.

Source/modules/encryptedmedia/MediaKeySession.cpp

Index: Source/modules/encryptedmedia/MediaKeySession.cpp
diff --git a/Source/modules/encryptedmedia/MediaKeySession.cpp b/Source/modules/encryptedmedia/MediaKeySession.cpp
index 11bf85103dbdc094e385de86c42442f42fd56c9e..cfe1ba88c1888cbd52052271cff141d141c90a03 100644
--- a/Source/modules/encryptedmedia/MediaKeySession.cpp
+++ b/Source/modules/encryptedmedia/MediaKeySession.cpp
@@ -71,14 +71,14 @@ MediaKeySession::MediaKeySession(ExecutionContext* context, blink::WebContentDec
     : ActiveDOMObject(context)
     , m_keySystem(keys->keySystem())
     , m_asyncEventQueue(GenericEventQueue::create(this))
-    , m_session(adoptPtr(cdm->createSession(this)))
+    , m_session(adoptPtr(cdm->createSession()))
     , m_keys(keys)
     , m_isClosed(false)
     , m_actionTimer(this, &MediaKeySession::actionTimerFired)
 {
     WTF_LOG(Media, "MediaKeySession::MediaKeySession");
     ScriptWrappable::init(this);
-    ASSERT(m_session);
+    m_session->setClientInterface(this);

[ddorwin, 2014/07/10 23:22:30]

The point of this change is to allow refactoring. Is there a reason not to do
that refactoring in this CL, which will land after the Chromium side anyway, so
that we can make sure the interface and Chromium changes enable that
refactoring?

[jrummell, 2014/07/11 00:55:53]

Without promises implemented, all responses come back as events. Need to
register the interface so we get something back.

 }
 
 MediaKeySession::~MediaKeySession()