Bug 1243415 - Check for a valid DOMWindow for screenshot in chrome scope. r=automatedtester

By the webdriver spec the code has to fail with a NoSuchWindowError if the
active window is no longer present.

MozReview-Commit-ID: HFl7yO5ErRn

--HG--
extra : rebase_source : 8d8271751a4cffdf4e74d4e66ff71588e7d2a01e

testing/marionette/driver.js

@@ -2408,9 +2408,14 @@ GeckoDriver.prototype.takeScreenshot = function (cmd, resp) {
   switch (this.context) {
     case Context.CHROME:
       let canvas;
-      let container = {frame: this.getCurrentWindow()};
       let highlightEls = [];
 
+      let container = {frame: this.getCurrentWindow().document.defaultView};
+
+      if (!container.frame) {
+        throw new NoSuchWindowError('Unable to locate window');
+      }
+
       for (let h of highlights) {
         let el = this.curBrowser.seenEls.get(h, container);
         highlightEls.push(el);