Add scroll threshold for app list for mouse wheel events.

ui/app_list/pagination_controller.cc

 // Copyright 2014 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_controller.h"
 
 #include "ui/app_list/pagination_model.h"
 #include "ui/events/event.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/vector2d.h"
@@ skipping 21 matching lines @@
   if (scroll_axis_ == SCROLL_AXIS_HORIZONTAL) {
     // If the view scrolls horizontally, both horizontal and vertical scroll
     // events are valid (since most mouse wheels only have vertical scrolling).
     offset_magnitude =
         abs(offset.x()) > abs(offset.y()) ? offset.x() : offset.y();
   } else {
     // If the view scrolls vertically, only vertical scroll events are valid.
     offset_magnitude = offset.y();
   }
 
-  // Do not scroll on very small touchpad events. Mouse wheel events should
-  // scroll, no matter how small the value change.
-  if (type == SCROLL_MOUSE_WHEEL ||
-      abs(offset_magnitude) > kMinScrollToSwitchPage) {
+  // Do not scroll on very small events.
+  // TODO(calamity): This should only apply on touchpad scroll but touchpad
+  // events are coming in as mousewheel events. See https://crbug.com/594264.
+  if (abs(offset_magnitude) > kMinScrollToSwitchPage) {
     if (!pagination_model_->has_transition()) {
       pagination_model_->SelectPageRelative(offset_magnitude > 0 ? -1 : 1,
                                             true);
     }
     return true;
   }
 
   return false;
 }
 
@@ skipping 27 matching lines @@
       if (fabs(velocity) > kMinHorizVelocityToSwitchPage)
         pagination_model_->SelectPageRelative(velocity < 0 ? 1 : -1, true);
       return true;
     }
     default:
       return false;
   }
 }
 
 }  // namespace app_list