Converts Widget::SetOpacity from char to float

ui/views/widget/native_widget_mac.mm

 // 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 "ui/views/widget/native_widget_mac.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include <utility>
 
@@ skipping 476 matching lines @@
   if (!bridge_ || fullscreen == IsFullscreen())
     return;
 
   bridge_->ToggleDesiredFullscreenState();
 }
 
 bool NativeWidgetMac::IsFullscreen() const {
   return bridge_ && bridge_->target_fullscreen_state();
 }
 
-void NativeWidgetMac::SetOpacity(unsigned char opacity) {
-  [GetNativeWindow() setAlphaValue:opacity / 255.0];
+void NativeWidgetMac::SetOpacity(float opacity) {
+  [GetNativeWindow() setAlphaValue:opacity];
 }
 
 void NativeWidgetMac::FlashFrame(bool flash_frame) {
   NOTIMPLEMENTED();
 }
 
 void NativeWidgetMac::RunShellDrag(View* view,
                                    const ui::OSExchangeData& data,
                                    const gfx::Point& location,
                                    int operation,
@@ skipping 238 matching lines @@
   [[ViewsNSWindowCloseAnimator alloc] initWithWindow:window];
 }
 
 - (void)animationDidEnd:(NSAnimation*)animation {
   [window_ close];
   [animation_ setDelegate:nil];
   [self release];
 }
 
 @end