Bug 1266336 - Clarify expected usage of CDM wrapper - r=cpearce

Assert that the CDM wrapper is given a non-null CDM pointer.
(so GetCDM() doesn't need to be null-checked.)
Renamed WidevineVideoDecoder mCDM to mCDMWrapper, to avoid (my) confusion.
Assert that WidevineVideoDecoder is given a non-null CDM-wrapper pointer.
Assert that WidevineVideoDecoder only accesses the CDM before DecodingComplete.

Small optimization: Move aCDM into mCDM (to save an AddRef/Release pair).

MozReview-Commit-ID: yKupY067ly

--HG--
extra : rebase_source : 94140b423a04f28368de0831761406c145fad93e

dom/media/gmp/widevine-adapter/WidevineUtils.h

@@ -48,7 +48,9 @@ public:
 
   CDMWrapper(cdm::ContentDecryptionModule_8* aCDM)
     : mCDM(aCDM)
-  {}
+  {
+    MOZ_ASSERT(mCDM);
+  }
   cdm::ContentDecryptionModule_8* GetCDM() const { return mCDM; }
 private:
   cdm::ContentDecryptionModule_8* mCDM;

dom/media/gmp/widevine-adapter/WidevineVideoDecoder.cpp

@@ -14,14 +14,17 @@ using namespace cdm;
 namespace mozilla {
 
 WidevineVideoDecoder::WidevineVideoDecoder(GMPVideoHost* aVideoHost,
-                                           RefPtr<CDMWrapper> aCDM)
+                                           RefPtr<CDMWrapper> aCDMWrapper)
   : mVideoHost(aVideoHost)
-  , mCDM(aCDM)
+  , mCDMWrapper(Move(aCDMWrapper))
   , mExtraData(new MediaByteBuffer())
   , mSentInput(false)
 {
+  // Expect to start with a CDM wrapper, will release it in DecodingComplete().
+  MOZ_ASSERT(mCDMWrapper);
   Log("WidevineVideoDecoder created this=%p", this);
 
+  // Corresponding Release is in DecodingComplete().
   AddRef();
 }
 
@@ -233,10 +236,11 @@ void
 WidevineVideoDecoder::DecodingComplete()
 {
   Log("WidevineVideoDecoder::DecodingComplete()");
-  if (mCDM) {
+  if (mCDMWrapper) {
     CDM()->DeinitializeDecoder(kStreamTypeVideo);
-    mCDM = nullptr;
+    mCDMWrapper = nullptr;
   }
+  // Release that corresponds to AddRef() in constructor.
   Release();
 }
 

dom/media/gmp/widevine-adapter/WidevineVideoDecoder.h

@@ -25,7 +25,7 @@ public:
   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(WidevineVideoDecoder)
 
   WidevineVideoDecoder(GMPVideoHost* aVideoHost,
-                       RefPtr<CDMWrapper> aCDM);
+                       RefPtr<CDMWrapper> aCDMWrapper);
   void InitDecode(const GMPVideoCodec& aCodecSettings,
                   const uint8_t* aCodecSpecific,
                   uint32_t aCodecSpecificLength,
@@ -44,12 +44,17 @@ private:
 
   ~WidevineVideoDecoder();
 
-  cdm::ContentDecryptionModule_8* CDM() { return mCDM->GetCDM(); }
+  cdm::ContentDecryptionModule_8* CDM() const {
+    // CDM should only be accessed before 'DecodingComplete'.
+    MOZ_ASSERT(mCDMWrapper);
+    // CDMWrapper ensure the CDM is non-null, no need to check again.
+    return mCDMWrapper->GetCDM();
+  }
 
   bool ReturnOutput(WidevineVideoFrame& aFrame);
 
   GMPVideoHost* mVideoHost;
-  RefPtr<CDMWrapper> mCDM;
+  RefPtr<CDMWrapper> mCDMWrapper;
   RefPtr<MediaByteBuffer> mExtraData;
   RefPtr<MediaByteBuffer> mAnnexB;
   GMPVideoDecoderCallback* mCallback;