change overlay scrollbar hover show to hover fade in

cc/trees/layer_tree_settings.h

 // Copyright 2011 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.
 
 #ifndef CC_TREES_LAYER_TREE_SETTINGS_H_
 #define CC_TREES_LAYER_TREE_SETTINGS_H_
 
 #include <stddef.h>
 
 #include <vector>
@@ skipping 35 matching lines @@
 
   enum ScrollbarAnimator {
     NO_ANIMATOR,
     ANDROID_OVERLAY,
     AURA_OVERLAY,
   };
   ScrollbarAnimator scrollbar_animator = NO_ANIMATOR;
   base::TimeDelta scrollbar_show_delay;
   base::TimeDelta scrollbar_fade_out_delay;
   base::TimeDelta scrollbar_fade_out_resize_delay;
+  base::TimeDelta scrollbar_fade_in_duration;
   base::TimeDelta scrollbar_fade_out_duration;
   base::TimeDelta scrollbar_thinning_duration;
   SkColor solid_color_scrollbar_color = SK_ColorWHITE;
   bool timeout_and_draw_when_animation_checkerboards = true;
   bool layer_transforms_should_scale_layer_contents = false;
   bool layers_always_allowed_lcd_text = false;
   float minimum_contents_scale = 0.0625f;
   float low_res_contents_scale_factor = 0.25f;
   float top_controls_show_threshold = 0.5f;
   float top_controls_hide_threshold = 0.5f;
@@ skipping 42 matching lines @@
   LayerTreeDebugState initial_debug_state;
 
   // Indicates that the LayerTreeHost should defer commits unless it has a valid
   // LocalSurfaceId set.
   bool enable_surface_synchronization = false;
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_SETTINGS_H_