Don't show the progress bar on iPad

This CL doesn't show the progress bar during the loading of the page on
iPad.

Bug: 813073
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I94c2ca6b28906220aeaf7affca702bd36e49b0d8
Reviewed-on: https://chromium-review.googlesource.com/941223Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539820}

ios/chrome/browser/ui/toolbar/clean/toolbar_view_controller.mm

@@ -472,6 +472,10 @@ const CGFloat kScrollFadeDistance = 30;
   _loading = loading;
   self.view.reloadButton.hiddenInCurrentState = loading;
   self.view.stopButton.hiddenInCurrentState = !loading;
+
+  if (IsIPadIdiom())
+    return;
+
   if (!loading) {
     [self stopProgressBar];
   } else if (self.view.progressBar.hidden) {