Bug 993734: Stop pretending that the observer service is threadsafe. r=bsmedberg

xpcom/ds/nsObserverService.cpp

@@ -222,7 +222,7 @@ nsObserverService::Create(nsISupports* outer, const nsIID& aIID, void* *aInstanc
 
 #define NS_ENSURE_VALIDCALL \
     if (!NS_IsMainThread()) {                                     \
-        NS_ERROR("Using observer service off the main thread!");  \
+        MOZ_CRASH("Using observer service off the main thread!"); \
         return NS_ERROR_UNEXPECTED;                               \
     }                                                             \
     if (mShuttingDown) {                                          \

xpcom/ds/nsObserverService.h

@@ -27,7 +27,7 @@ public:
 
   nsObserverService();
 
-  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_ISUPPORTS
   NS_DECL_NSIOBSERVERSERVICE
   NS_DECL_NSIMEMORYREPORTER