Bug 1366930 - Correct error handling in mozilla::MediaShutdownManager::InitStatics. r=gerald

Resetting sInstance in MediaShutdownManager::InitStatics() will cause
MediaShutdownManager::Instance().Register() to crash immediately without
a chance to handle the error in Register().

Instead, we keep an error code to know whether to bail out in Register().

MozReview-Commit-ID: EGqL1407Gh

--HG--
extra : rebase_source : 055dfc35d854c93013067971f0c9f813c8654708

dom/media/MediaShutdownManager.cpp

@@ -78,7 +78,7 @@ MediaShutdownManager::InitStatics()
     NS_LITERAL_STRING("MediaShutdownManager shutdown"));
   if (NS_FAILED(rv)) {
     LOGW("Failed to add shutdown blocker! rv=%x", uint32_t(rv));
-    sInstance = nullptr;
+    sInstance->mError = rv;
   }
 }
 
@@ -99,7 +99,7 @@ nsresult
 MediaShutdownManager::Register(MediaDecoder* aDecoder)
 {
   MOZ_ASSERT(NS_IsMainThread());
-  if (!sInstance) {
+  if (NS_FAILED(mError)) {
     return NS_ERROR_NOT_INITIALIZED;
   }
   if (mIsDoingXPCOMShutDown) {

dom/media/MediaShutdownManager.h

@@ -83,6 +83,7 @@ private:
   nsTHashtable<nsRefPtrHashKey<MediaDecoder>> mDecoders;
 
   bool mIsDoingXPCOMShutDown = false;
+  nsresult mError = NS_OK;
 };
 
 } // namespace mozilla