Converts Widget::SetOpacity from char to float

ui/views/widget/desktop_aura/desktop_drag_drop_client_aurax11.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_drag_drop_client_aurax11.h"
 
 #include <X11/Xatom.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 110 matching lines @@
 // The time to wait since sending the last XdndPosition message before
 // reprocessing the most recent mouse move event in case that the window
 // stacking order has changed and |source_current_window_| needs to be updated.
 const int kRepeatMouseMoveTimeoutMs = 350;
 
 // The minimum alpha before we declare a pixel transparent when searching in
 // our source image.
 const uint32_t kMinAlpha = 32;
 
 // |drag_widget_|'s opacity.
-const unsigned char kDragWidgetOpacity = 0xc0;
+const float kDragWidgetOpacity = .75f;
 
 static base::LazyInstance<
     std::map< ::Window, views::DesktopDragDropClientAuraX11*> >::Leaky
         g_live_client_map = LAZY_INSTANCE_INITIALIZER;
 
 }  // namespace
 
 namespace views {
 
 DesktopDragDropClientAuraX11*
@@ skipping 1085 matching lines @@
     for (int x = 0; x < in_bitmap->width(); ++x) {
       if (SkColorGetA(in_row[x]) > kMinAlpha)
         return true;
     }
   }
 
   return false;
 }
 
 }  // namespace views