Pass scroll bar placement as an enum instead of std::string

Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 40 matching lines @@
 static int cButtonLength[] = { 14, 10 };
 static int cScrollbarThickness[] = { 15, 11 };
 static int cButtonInset[] = { 14, 11 };
 static int cThumbMinLength[] = { 26, 20 };
 
 static int cOuterButtonLength[] = { 16, 14 }; // The outer button in a double button pair is a bit bigger.
 static int cOuterButtonOverlap = 2;
 
 static ScrollbarButtonsPlacement gButtonPlacement = ScrollbarButtonsDoubleEnd;
 
-void ScrollbarThemeMacNonOverlayAPI::updateButtonPlacement(const std::string& buttonPlacement)
+void ScrollbarThemeMacNonOverlayAPI::updateButtonPlacement(ScrollbarButtonsPlacement buttonPlacement)
 {
-    if (buttonPlacement == "Single")
-        gButtonPlacement = ScrollbarButtonsSingle;
-    else if (buttonPlacement == "DoubleMin")
-        gButtonPlacement = ScrollbarButtonsDoubleStart;
-    else if (buttonPlacement == "DoubleBoth")
-        gButtonPlacement = ScrollbarButtonsDoubleBoth;
-    else
-        gButtonPlacement = ScrollbarButtonsDoubleEnd;
+    gButtonPlacement = buttonPlacement;
 }
 
 // Override ScrollbarThemeMacCommon::paint() to add support for the following:
 //     - drawing using WebThemeEngine functions
 //     - drawing tickmarks
 //     - Skia specific changes
 bool ScrollbarThemeMacNonOverlayAPI::paint(ScrollbarThemeClient* scrollbar, GraphicsContext* context, const IntRect& damageRect)
 {
     DisplayItem::Type displayItemType = scrollbar->orientation() == HorizontalScrollbar ? DisplayItem::ScrollbarHorizontal : DisplayItem::ScrollbarVertical;
     if (DrawingRecorder::useCachedDrawingIfPossible(*context, *scrollbar, displayItemType))
@@ skipping 235 matching lines @@
         return IntRect(scrollbar->x() + startWidth, scrollbar->y(), scrollbar->width() - totalWidth, thickness);
     return IntRect(scrollbar->x(), scrollbar->y() + startWidth, thickness, scrollbar->height() - totalWidth);
 }
 
 int ScrollbarThemeMacNonOverlayAPI::minimumThumbLength(ScrollbarThemeClient* scrollbar)
 {
     return cThumbMinLength[scrollbar->controlSize()];
 }
 
 }