Bug 1281750 - Marionette should include current application process id in capabilities. r=automatedtester

MozReview-Commit-ID: L9tdmHfUZEY

--HG--
extra : rebase_source : d46b87e50500f2e5dc793b9aaf922f1be661a323

testing/marionette/driver.js

@@ -151,6 +151,7 @@ this.GeckoDriver = function(appName, device, stopSignal) {
     "XULappId" : Services.appinfo.ID,
     "appBuildId" : Services.appinfo.appBuildID,
     "device": device,
+    "processId" : Services.appinfo.processID,
     "version": Services.appinfo.version,
   };