Bug 1277090: Have Marionette return only attributes from getElementAttribute. r=ato

Using the Selenium atom we are conflating properties and attributes which is not
thing we really want to be doing.

MozReview-Commit-ID: HdZOz1jQrwz

--HG--
extra : rebase_source : 70118dba39bb1a72e78a264d2a71beff3671f9cb

testing/marionette/driver.js

@@ -1786,7 +1786,16 @@ GeckoDriver.prototype.getElementAttribute = function*(cmd, resp) {
     case Context.CHROME:
       let win = this.getCurrentWindow();
       let el = this.curBrowser.seenEls.get(id, {frame: win});
-      resp.body.value = atom.getElementAttribute(el, name, this.getCurrentWindow());
+
+      if (element.isBooleanAttribute(el, name)) {
+        if (el.hasAttribute(name)) {
+          resp.body.value = "true";
+        } else {
+          resp.body.value = null;
+        }
+      } else {
+        resp.body.value = el.getAttribute(name);
+      }
       break;
 
     case Context.CONTENT: