Fix stroke color definition of canvas context.

Source/core/html/canvas/CanvasStyle.cpp

Index: Source/core/html/canvas/CanvasStyle.cpp
diff --git a/Source/core/html/canvas/CanvasStyle.cpp b/Source/core/html/canvas/CanvasStyle.cpp
index cfb5c4f270895738467b47b527e2f5c808a71285..192f8b6c14e07db38c3479d91f3e97e86fc8a76c 100644
--- a/Source/core/html/canvas/CanvasStyle.cpp
+++ b/Source/core/html/canvas/CanvasStyle.cpp
@@ -148,6 +148,7 @@ PassRefPtrWillBeRawPtr<CanvasStyle> CanvasStyle::createFromStringWithOverrideAlp
     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));