Fix stroke color definition of canvas context.

Source/core/html/canvas/CanvasStyle.cpp

 /*
  * Copyright (C) 2006, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 130 matching lines @@
         return nullptr;
     }
 }
 
 PassRefPtrWillBeRawPtr<CanvasStyle> CanvasStyle::createFromStringWithOverrideAlpha(const String& color, float alpha)
 {
     RGBA32 rgba;
     ColorParseResult parseResult = parseColor(rgba, color);
     switch (parseResult) {
     case ParsedRGBA:
+    case ParsedSystemColor:
         return adoptRefWillBeNoop(new CanvasStyle(colorWithOverrideAlpha(rgba, alpha)));
     case ParsedCurrentColor:
         return adoptRefWillBeNoop(new CanvasStyle(CurrentColorWithOverrideAlpha, alpha));
     case ParseFailed:
         return nullptr;
     default:
         ASSERT_NOT_REACHED();
         return nullptr;
     }
 }
@@ skipping 111 matching lines @@
     }
 }
 
 void CanvasStyle::trace(Visitor* visitor)
 {
     visitor->trace(m_gradient);
     visitor->trace(m_pattern);
 }
 
 }