MacViews: Handle System colors that have no alpha channel

ui/native_theme/native_theme_mac.mm

 // Copyright (c) 2013 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/native_theme/native_theme_mac.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/basictypes.h"
 #include "base/mac/mac_util.h"
@@ skipping 79 matching lines @@
   if (device_color)
     return gfx::NSDeviceColorToSkColor(device_color);
 
   // Sometimes the conversion is not possible, but we can get an approximation
   // by going through a CGColorRef. Note that simply using NSColor methods for
   // accessing components for system colors results in exceptions like
   // "-numberOfComponents not valid for the NSColor NSNamedColorSpace System
   // windowBackgroundColor; need to first convert colorspace." Hence the
   // conversion first to CGColor.
   CGColorRef cg_color = [color CGColor];
-  if (CGColorGetNumberOfComponents(cg_color) == 4)
+  const size_t component_count = CGColorGetNumberOfComponents(cg_color);
+  if (component_count == 4)
     return gfx::CGColorRefToSkColor(cg_color);
 
-  CHECK_EQ(2u, CGColorGetNumberOfComponents(cg_color));
-  // Two components means a grayscale channel and an alpha channel, which
+  CHECK(component_count == 1 || component_count == 2);
+  // 1-2 components means a grayscale channel and maybe an alpha channel, which
   // CGColorRefToSkColor will not like. But RGB is additive, so the conversion
   // is easy (RGB to grayscale is less easy).
   const CGFloat* components = CGColorGetComponents(cg_color);
-  return SkColorSetARGB(SkScalarRoundToInt(255.0 * components[1]),
+  CGFloat alpha = component_count == 2 ? components[1] : 1.0;
+  return SkColorSetARGB(SkScalarRoundToInt(255.0 * alpha),
                         SkScalarRoundToInt(255.0 * components[0]),
                         SkScalarRoundToInt(255.0 * components[0]),
                         SkScalarRoundToInt(255.0 * components[0]));
 }
 
 }  // namespace
 
 namespace ui {
 
 // static
@@ skipping 242 matching lines @@
   set_scrollbar_button_length(0);
   SetScrollbarColors(kScrollerThumbColor,
                      kScrollerThumbHoverColor,
                      kScrollerTrackGradientColors[0]);
 }
 
 NativeThemeMac::~NativeThemeMac() {
 }
 
 }  // namespace ui