Bug 1443177 - Support 'verify' in reftest sandbox; r=jmaher

layout/tools/reftest/manifest.jsm

@@ -563,6 +563,9 @@ sandbox.compareRetainedDisplayLists = g.compareRetainedDisplayLists;
     // Graphics features
     sandbox.usesRepeatResampling = sandbox.d2d;
 
+    // Running in a test-verify session?
+    sandbox.verify = prefs.getBoolPref("reftest.verify", false);
+
     if (!g.dumpedConditionSandbox) {
         g.logger.info("Dumping JSON representation of sandbox");
         g.logger.info(JSON.stringify(Cu.waiveXrays(sandbox)));