Bug 1285898 - [e10s-multi] fixup PContent ordering via immediate event dispatch. r=baku

dom/ipc/ContentChild.cpp

@@ -3046,7 +3046,7 @@ ContentChild::RecvDispatchLocalStorageChange(const nsString& aDocumentURI,
 {
   Storage::DispatchStorageEvent(Storage::LocalStorage,
                                 aDocumentURI, aKey, aOldValue, aNewValue,
-                                aPrincipal, aIsPrivate, nullptr);
+                                aPrincipal, aIsPrivate, nullptr, true);
   return IPC_OK();
 }
 

dom/storage/Storage.cpp

@@ -231,7 +231,7 @@ Storage::BroadcastChangeNotification(const nsSubstring& aKey,
   }
 
   DispatchStorageEvent(GetType(), mDocumentURI, aKey, aOldValue, aNewValue,
-                       mPrincipal, mIsPrivate, this);
+                       mPrincipal, mIsPrivate, this, false);
 }
 
 /* static */ void
@@ -242,7 +242,8 @@ Storage::DispatchStorageEvent(StorageType aStorageType,
                               const nsAString& aNewValue,
                               nsIPrincipal* aPrincipal,
                               bool aIsPrivate,
-                              Storage* aStorage)
+                              Storage* aStorage,
+                              bool aImmediateDispatch)
 {
   StorageEventInit dict;
   dict.mBubbles = false;
@@ -266,7 +267,12 @@ Storage::DispatchStorageEvent(StorageType aStorageType,
                                   ? u"localStorage"
                                   : u"sessionStorage",
                                 aIsPrivate);
+
+  if (aImmediateDispatch) {
+    Unused << r->Run();
+  } else {
     NS_DispatchToMainThread(r);
+  }
 
   // If we are in the parent process and we have the principal, we want to
   // broadcast this event to every other process.

dom/storage/Storage.h

@@ -131,6 +131,13 @@ public:
   }
 
   // aStorage can be null if this method is called by ContentChild.
+  //
+  // aImmediateDispatch is for use by (main-thread) IPC code so that PContent
+  // ordering can be maintained.  Without this, the event would be enqueued and
+  // run in a future turn of the event loop, potentially allowing other PContent
+  // Recv* methods to trigger script that wants to assume our localstorage
+  // changes have already been applied.  This is the case for message manager
+  // messages which are used by ContentTask testing logic and webextensions.
   static void
   DispatchStorageEvent(StorageType aStorageType,
                        const nsAString& aDocumentURI,
@@ -139,7 +146,8 @@ public:
                        const nsAString& aNewValue,
                        nsIPrincipal* aPrincipal,
                        bool aIsPrivate,
-                       Storage* aStorage);
+                       Storage* aStorage,
+                       bool aImmediateDispatch);
 
   void
   ApplyEvent(StorageEvent* aStorageEvent);