app_list: Improve visual feedback for invalid touch scroll.

ui/app_list/pagination_model.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/app_list/pagination_model.h"
 
 #include <algorithm>
 
 #include "ui/app_list/pagination_model_observer.h"
 #include "ui/base/animation/slide_animation.h"
@@ skipping 89 matching lines @@
     transition_.target_page = CalculateTargetPage(page_change_dir);
 
   // Updates transition progress.
   int transition_dir = transition_.target_page > selected_page_ ? 1 : -1;
   double progress = transition_.progress +
       fabs(delta) * page_change_dir * transition_dir;
 
   if (progress < 0) {
     clear_transition();
   } else if (progress > 1) {
-    if (is_valid_page(transition_.target_page))
+    if (is_valid_page(transition_.target_page)) {
       SelectPage(transition_.target_page, false);
-    clear_transition();
+      clear_transition();
+    }
   } else {
     transition_.progress = progress;
     NotifyTransitionChanged();
   }
 }
 
 void PaginationModel::EndScroll() {
   if (!has_transition())
     return;
 
@@ skipping 94 matching lines @@
   } else if (transition_animation_->GetCurrentValue() == 0) {
     // Hiding animation ends. No page change should happen.
     ResetTranstionAnimation();
   }
 
   if (next_target >= 0)
     SelectPage(next_target, true);
 }
 
 }  // namespace app_list