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

ash/wm/overview/window_grid.cc

Index: ash/wm/overview/window_grid.cc
diff --git a/ash/wm/overview/window_grid.cc b/ash/wm/overview/window_grid.cc
index 72a6743911ec1c0cfb1a51cfe65c7e01b0c7d7b8..b04962c14c4ed764dc5d8b5e1904822d48d88983 100644
--- a/ash/wm/overview/window_grid.cc
+++ b/ash/wm/overview/window_grid.cc
@@ -435,7 +435,7 @@ void WindowGrid::InitSelectionWidget(WindowSelector::Direction direction) {
       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 =
@@ -472,7 +472,7 @@ void WindowGrid::MoveSelectionWidget(WindowSelector::Direction direction,
     // 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();