Bug 1523013 - Clear SamplesWaitingForKey::mProxy in Shutdown(). r=cpearce

There's a strong cycle of references between SamplesWaitingForKey and
CDMProxy that does not get cleared unless keys actually come in. This
causes a leak. One way to avoid that leak is to clear the proxy
reference when the things holding the SamplesWaitingForKey is shut
down.

Differential Revision: https://phabricator.services.mozilla.com/D17960

--HG--
extra : moz-landing-system : lando

dom/media/platforms/agnostic/eme/EMEDecoderModule.cpp

@@ -251,6 +251,7 @@ class EMEDecryptor : public MediaDataDecoder,
     return InvokeAsync(mTaskQueue, __func__, [self, this]() {
       MOZ_ASSERT(!mIsShutdown);
       mIsShutdown = true;
+      mSamplesWaitingForKey->BreakCycles();
       mSamplesWaitingForKey = nullptr;
       RefPtr<MediaDataDecoder> decoder = mDecoder.forget();
       mProxy = nullptr;
@@ -347,6 +348,7 @@ RefPtr<MediaDataDecoder::FlushPromise> EMEMediaDataDecoderProxy::Flush() {
 RefPtr<ShutdownPromise> EMEMediaDataDecoderProxy::Shutdown() {
   RefPtr<EMEMediaDataDecoderProxy> self = this;
   return InvokeAsync(mThread, __func__, [self, this]() {
+    mSamplesWaitingForKey->BreakCycles();
     mSamplesWaitingForKey = nullptr;
     mProxy = nullptr;
     return MediaDataDecoderProxy::Shutdown();

dom/media/platforms/agnostic/eme/SamplesWaitingForKey.cpp

@@ -69,4 +69,9 @@ void SamplesWaitingForKey::Flush() {
   mSamples.Clear();
 }
 
+void SamplesWaitingForKey::BreakCycles() {
+  MutexAutoLock lock(mMutex);
+  mProxy = nullptr;
+}
+
 }  // namespace mozilla

dom/media/platforms/agnostic/eme/SamplesWaitingForKey.h

@@ -42,6 +42,8 @@ class SamplesWaitingForKey {
 
   void Flush();
 
+  void BreakCycles();
+
  protected:
   ~SamplesWaitingForKey();