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

ui/views/widget/widget_unittest.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 <algorithm>
 #include <memory>
 #include <set>
 
 #include "base/bind.h"
 #include "base/macros.h"
@@ skipping 632 matching lines @@
     widget->Activate();
     widget->Deactivate();
     widget->IsActive();
     widget->SetAlwaysOnTop(true);
     widget->IsAlwaysOnTop();
     widget->Maximize();
     widget->Minimize();
     widget->Restore();
     widget->IsMaximized();
     widget->IsFullscreen();
-    widget->SetOpacity(0);
+    widget->SetOpacity(0.f);
     widget->FlashFrame(true);
     widget->IsVisible();
     widget->GetThemeProvider();
     widget->GetNativeTheme();
     widget->GetFocusManager();
     widget->SchedulePaintInRect(gfx::Rect(0, 0, 1, 2));
     widget->IsMouseEventsEnabled();
     widget->SetNativeWindowProperty("xx", widget);
     widget->GetNativeWindowProperty("xx");
     widget->GetFocusTraversable();
@@ skipping 3047 matching lines @@
   EXPECT_FALSE(!!IsWindow(owned_hwnd));
   EXPECT_TRUE(!!IsWindowEnabled(top_hwnd));
 
   top_level_widget.CloseNow();
 }
 
 #endif  // defined(OS_WIN)
 
 }  // namespace test
 }  // namespace views