Bug 1562948: Use a multi-threaded apartment inside AnnotateWMIData_ThreadStart; r=mhowell

Using a single-threaded apartment creates a race condition that triggers a
crash in a11y when it hooks InSendMessageEx. Since we're on a background thread,
we don't have a strongly compelling reason to use an STA when an MTA will work
just fine.

Differential Revision: https://phabricator.services.mozilla.com/D36677

--HG--
extra : moz-landing-system : lando

toolkit/xre/nsAppRunner.cpp

@@ -3601,15 +3601,12 @@ static void AnnotateWMIData() {
 }
 
 static void PR_CALLBACK AnnotateWMIData_ThreadStart(void*) {
-  HRESULT hr = CoInitialize(nullptr);
-
-  if (FAILED(hr)) {
+  mscom::MTARegion mta;
+  if (!mta.IsValid()) {
     return;
   }
 
   AnnotateWMIData();
-
-  CoUninitialize();
 }
 #endif  // XP_WIN