Converts Widget::SetOpacity from char to float

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.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 "ui/views/widget/desktop_aura/desktop_window_tree_host_x11.h"
 
 #include <X11/Xatom.h>
 #include <X11/Xregion.h>
 #include <X11/Xutil.h>
 #include <X11/extensions/XInput2.h>
@@ skipping 832 matching lines @@
     ResetWindowRegion();
   }
   // Else: the widget will be relaid out either when the window bounds change or
   // when |xwindow_|'s fullscreen state changes.
 }
 
 bool DesktopWindowTreeHostX11::IsFullscreen() const {
   return is_fullscreen_;
 }
 
-void DesktopWindowTreeHostX11::SetOpacity(unsigned char opacity) {
+void DesktopWindowTreeHostX11::SetOpacity(float opacity) {
   // X server opacity is in terms of 32 bit unsigned int space, and counts from
   // the opposite direction.
   // XChangeProperty() expects "cardinality" to be long.
-  unsigned long cardinality = opacity * 0x1010101;
+  unsigned long cardinality = static_cast<int>(opacity * 255) * 0x1010101;
 
   if (cardinality == 0xffffffff) {
     XDeleteProperty(xdisplay_, xwindow_,
                     atom_cache_.GetAtom("_NET_WM_WINDOW_OPACITY"));
   } else {
     XChangeProperty(xdisplay_, xwindow_,
                     atom_cache_.GetAtom("_NET_WM_WINDOW_OPACITY"),
                     XA_CARDINAL, 32,
                     PropModeReplace,
                     reinterpret_cast<unsigned char*>(&cardinality), 1);
@@ skipping 1185 matching lines @@
   if (linux_ui) {
     ui::NativeTheme* native_theme = linux_ui->GetNativeTheme(window);
     if (native_theme)
       return native_theme;
   }
 
   return ui::NativeThemeAura::instance();
 }
 
 }  // namespace views