b=317351, add env var to disable windows crash dialog on crash, r=bsmedberg

toolkit/xre/nsAppRunner.cpp

@@ -1842,7 +1842,16 @@ XRE_main(int argc, char* argv[], const nsXREAppData* aAppData)
   // Suppress the "DLL Foo could not be found" dialog, such that if dependent
   // libraries (such as GDI+) are not preset, we gracefully fail to load those
   // XPCOM components, instead of being ungraceful.
-  SetErrorMode(SEM_FAILCRITICALERRORS);
+  UINT realMode = SetErrorMode(0);
+  realMode |= SEM_FAILCRITICALERRORS;
+  // If XRE_NO_WINDOWS_CRASH_DIALOG is set, suppress displaying the "This
+  // application has crashed" dialog box.  This is mainly useful for
+  // automated testing environments, e.g. tinderbox, where there's no need
+  // for a dozen of the dialog boxes to litter the console
+  if (getenv("XRE_NO_WINDOWS_CRASH_DIALOG"))
+    realMode |= SEM_NOGPFAULTERRORBOX | SEM_NOOPENFILEERRORBOX;
+
+  SetErrorMode(realMode);
 
 #ifdef DEBUG
   // Disable small heap allocator to get heapwalk() giving us