Bug 1266336 - Check sCDMWrapper before creating video decoder - r=cpearce

Ensure that there is a CDM before creating a video decoder that relies on that
CDM. This is mainly to prevent using the Widevine video decoder alone, without
decryption.

MozReview-Commit-ID: 7p49CnmV2r7

--HG--
extra : rebase_source : 49b07100b2be56584bc14f41d39d4872f0539c3a

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

@@ -124,7 +124,13 @@ WidevineAdapter::GMPGetAPI(const char* aAPIName,
     *aPluginAPI = decryptor;
 
   } else if (!strcmp(aAPIName, GMP_API_VIDEO_DECODER)) {
-    *aPluginAPI = new WidevineVideoDecoder(static_cast<GMPVideoHost*>(aHostAPI), RefPtr<CDMWrapper>(sCDMWrapper));
+    if (!sCDMWrapper) {
+      Log("WidevineAdapter::GMPGetAPI(%s, 0x%p, 0x%p) this=0x%p No cdm for video decoder",
+          aAPIName, aHostAPI, aPluginAPI, this);
+      return GMPGenericErr;
+    }
+    *aPluginAPI = new WidevineVideoDecoder(static_cast<GMPVideoHost*>(aHostAPI),
+                                           RefPtr<CDMWrapper>(sCDMWrapper));
 
   }
   return *aPluginAPI ? GMPNoErr : GMPNotImplementedErr;