Bug 1329669 Gracefully handle nullptr Cache actor in CacheStorage::Open() result. r=asuth

dom/bindings/Errors.msg

@@ -100,3 +100,4 @@ MSG_DEF(MSG_TIME_VALUE_OUT_OF_RANGE, 1, JSEXN_TYPEERR, "{0} is outside the suppo
 MSG_DEF(MSG_ONLY_IF_CACHED_WITHOUT_SAME_ORIGIN, 1, JSEXN_TYPEERR, "Request mode '{0}' was used, but request cache mode 'only-if-cached' can only be used with request mode 'same-origin'.")
 MSG_DEF(MSG_THRESHOLD_RANGE_ERROR, 0, JSEXN_RANGEERR, "Threshold values must all be in the range [0, 1].")
 MSG_DEF(MSG_WORKER_THREAD_SHUTTING_DOWN, 0, JSEXN_TYPEERR, "The Worker thread is shutting down.")
+MSG_DEF(MSG_CACHE_OPEN_FAILED, 0, JSEXN_TYPEERR, "CacheStorage.open() failed to access the storage system.")

dom/cache/CacheOpChild.cpp

@@ -155,6 +155,17 @@ CacheOpChild::Recv__delete__(const ErrorResult& aRv,
     {
       auto actor = static_cast<CacheChild*>(
         aResult.get_StorageOpenResult().actorChild());
+
+      // If we have a success status then we should have an actor.  Gracefully
+      // reject instead of crashing, though, if we get a nullptr here.
+      MOZ_DIAGNOSTIC_ASSERT(actor);
+      if (!actor) {
+        ErrorResult status;
+        status.ThrowTypeError<MSG_CACHE_OPEN_FAILED>();
+        mPromise->MaybeReject(status);
+        break;
+      }
+
       actor->SetWorkerHolder(GetWorkerHolder());
       RefPtr<Cache> cache = new Cache(mGlobal, actor);
       mPromise->MaybeResolve(cache);

dom/cache/Manager.cpp

@@ -1215,6 +1215,7 @@ public:
                                         &cacheFound, &mCacheId);
     if (NS_WARN_IF(NS_FAILED(rv))) { return rv; }
     if (cacheFound) {
+      MOZ_DIAGNOSTIC_ASSERT(mCacheId != INVALID_CACHE_ID);
       return rv;
     }
 
@@ -1227,12 +1228,14 @@ public:
     rv = trans.Commit();
     if (NS_WARN_IF(NS_FAILED(rv))) { return rv; }
 
+    MOZ_DIAGNOSTIC_ASSERT(mCacheId != INVALID_CACHE_ID);
     return rv;
   }
 
   virtual void
   Complete(Listener* aListener, ErrorResult&& aRv) override
   {
+    MOZ_DIAGNOSTIC_ASSERT(aRv.Failed() || mCacheId != INVALID_CACHE_ID);
     aListener->OnOpComplete(Move(aRv), StorageOpenResult(), mCacheId);
   }