Widget opacity goes from 0 to 1, not 0 to 255.

ash/wm/overview/window_grid.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 "ash/wm/overview/window_grid.h"
 
 #include <algorithm>
 #include <functional>
 #include <set>
 #include <utility>
@@ skipping 417 matching lines @@
   views::View* content_view = new views::View;
   content_view->set_background(
       views::Background::CreateSolidBackground(kWindowSelectionColor));
   content_view->SetBorder(views::Border::CreateSolidBorder(
       kWindowSelectionBorderThickness, kWindowSelectionBorderColor));
   selection_widget_->SetContentsView(content_view);
   selection_widget_window->GetParent()->StackChildAtBottom(
       selection_widget_window);
   selection_widget_->Show();
   // New selection widget starts with 0 opacity and then fades in.
-  selection_widget_window->SetOpacity(0);
+  selection_widget_window->SetOpacity(0.f);
 
   const gfx::Rect target_bounds = SelectedWindow()->target_bounds();
   gfx::Vector2d fade_out_direction =
           GetSlideVectorForFadeIn(direction, target_bounds);
   display::Display dst_display =
       display::Screen::GetScreen()->GetDisplayMatching(target_bounds);
   selection_widget_window->SetBoundsInScreen(target_bounds - fade_out_direction,
                                              dst_display);
 }
 
@@ skipping 16 matching lines @@
     animation_settings.SetTransitionDuration(
         base::TimeDelta::FromMilliseconds(
             kOverviewSelectorTransitionMilliseconds));
     animation_settings.SetPreemptionStrategy(
         ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
     animation_settings.SetTweenType(gfx::Tween::FAST_OUT_LINEAR_IN);
     // CleanupWidgetAfterAnimationObserver will delete itself (and the
     // widget) when the movement animation is complete.
     animation_settings.AddObserver(
         new CleanupWidgetAfterAnimationObserver(std::move(selection_widget_)));
-    old_selection->SetOpacity(0);
+    old_selection->SetOpacity(0.f);
     old_selection_window->SetBounds(old_selection_window->GetBounds() +
                                     fade_out_direction);
     old_selection->Hide();
   }
   if (out_of_bounds)
     return;
 
   if (!selection_widget_)
     InitSelectionWidget(direction);
   // Send an a11y alert so that if ChromeVox is enabled, the item label is
@@ skipping 17 matching lines @@
         ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
     selection_widget_->SetBounds(SelectedWindow()->target_bounds());
     selection_widget_->SetOpacity(1.f);
     return;
   }
   selection_widget_->SetBounds(SelectedWindow()->target_bounds());
   selection_widget_->SetOpacity(1.f);
 }
 
 }  // namespace ash