Enable XPC_CHECK_WRAPPER_THREADSAFETY in release builds and make it force a failure from XPCWrappedNative::FinishInit (612745, r=gal).

js/src/xpconnect/src/xpcprivate.h

@@ -179,8 +179,8 @@ static FARPROC GetProcAddressA(HMODULE hMod, wchar_t *procName);
 
 #ifdef DEBUG
 #define XPC_DETECT_LEADING_UPPERCASE_ACCESS_ERRORS
-#define XPC_CHECK_WRAPPER_THREADSAFETY
 #endif
+#define XPC_CHECK_WRAPPER_THREADSAFETY
 
 #if defined(DEBUG_xpc_hacker)
 #define XPC_DUMP_AT_SHUTDOWN

js/src/xpconnect/src/xpcwrappednative.cpp

@@ -1202,8 +1202,11 @@ XPCWrappedNative::FinishInit(XPCCallContext &ccx)
     mThread = do_GetCurrentThread();
 
     if(HasProto() && GetProto()->ClassIsMainThreadOnly() && !NS_IsMainThread())
+    {
         DEBUG_ReportWrapperThreadSafetyError(ccx,
             "MainThread only wrapper created on the wrong thread", this);
+        return JS_FALSE;
+    }
 #endif
 
     // A hack for bug 517665, increase the probability for GC.
@@ -1511,7 +1514,8 @@ XPCWrappedNative::ReparentWrapperIfFound(XPCCallContext& ccx,
     if (!XPCPerThreadData::IsMainThread(ccx) ||
         (wrapper &&
          wrapper->GetProto() &&
-         !wrapper->GetProto()->ClassIsMainThreadOnly())) {
+         !wrapper->GetProto()->ClassIsMainThreadOnly()))
+    {
         return NS_ERROR_FAILURE;
     }