import changes from `dev' branch of rmottola/Arctic-Fox:

- Bug 622657 - catch invalid bookmark items and delete them when syncing bookmarks. r=rnewman (bd91e14c9a)
- Bug 1166853 - Sync "hangs" when trying to apply a livemark to a reconciled folder. r=rnewman (94a6a19753)
- Bug 1012597 - Part 1: provide a way to invalidate the Places GUIDs cache. r=rnewman (66f43cb831)
- Bug 1012597 - Part 2: ensure Sync invalidates the Places GUIDs cache when needed. r=rnewman (2a67b0dfa8)
- Bug 1182366 - avoid an invalid bookmark from preventing all bookmarks syncing. r=rnewman (df895d4c35)
- let -> var (e9c382c761)
- Bug 1188170 - log the url string when the Sync bookmarks engine fails to get a URI. r=rnewman (424e5405f7)
- Bug 1195603 - prevent Sync from blocking app shutdown. r=rnewman (94c3091f9c)
- Bug 1183934 - only log an error saving JSON if an error actually occurred. r=rnewman (6b4358035c)
- Bug 1198385 - Use MFBT guard macros in the editor guard objects; r=froydnj (72e5e9f66f)
- Bug 1198385 follow-up: Fix the build bustage on a CLOSED TREE (d626e56e92)
- Bug 1177013 - Use CancelCurrentTransaction to avoid crashes (r=dvander) (362e5fc343)
- Bug 1154990 - Better error messages when IPC send fails (r=bent) (b311fb94aa)
- Bug 1177013 - Avoid memory leaks when returning errors from IPC Send (r=dvander) (f453a8feb5)
- Bug 1176096 - Ensure we don't do self-moves in move assignment (r=bent) (31aca4ad89)
- Bug 1177013 - Crash in IPC situations where we don't know what to do (r=dvander) (0e86cc437e)
- Bug 1185639 - Allow deferred message processing to happen between consecutive IPC message dispatches. r=jimm (7782c9caaf)

xpcom/threads/nsThread.cpp

@@ -723,8 +723,9 @@ nsThread::ProcessNextEvent(bool aMayWait, bool* aResult)
 
 #if !defined(MOZILLA_XPCOMRT_API)
   // If we're on the main thread, we shouldn't be dispatching CPOWs.
-  MOZ_RELEASE_ASSERT(mIsMainThread != MAIN_THREAD ||
-                     !ipc::ParentProcessIsBlocked());
+  if (mIsMainThread == MAIN_THREAD) {
+    ipc::CancelCPOWs();
+  }
 #endif // !defined(MOZILLA_XPCOMRT_API)
 
   if (NS_WARN_IF(PR_GetCurrentThread() != mThread)) {