Bug 1257526 - Harmonise unsupported operation error usage; r=automatedtester

Throw unsupported operation errors the same way throughout Marionette.

MozReview-Commit-ID: D63gVIeX2qK

--HG--
extra : rebase_source : 2f93a7a847c599234a1303a27a59a64f74e8f3f6

testing/marionette/driver.js

@@ -2647,8 +2647,8 @@ GeckoDriver.prototype.getWindowSize = function(cmd, resp) {
  * in the window being in the maximized state.
  */
 GeckoDriver.prototype.setWindowSize = function(cmd, resp) {
-  if (this.appName !== "Firefox") {
-    throw new UnsupportedOperationError("Not supported on mobile");
+  if (this.appName != "Firefox") {
+    throw new UnsupportedOperationError();
   }
 
   let width = parseInt(cmd.parameters.width);
@@ -2670,7 +2670,7 @@ GeckoDriver.prototype.setWindowSize = function(cmd, resp) {
  */
 GeckoDriver.prototype.maximizeWindow = function(cmd, resp) {
   if (this.appName != "Firefox") {
-    throw new UnsupportedOperationError("Not supported for mobile");
+    throw new UnsupportedOperationError();
   }
 
   let win = this.getCurrentWindow();