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

Source/web/mac/WebScrollbarTheme.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 42 matching lines @@
     if (!animation_initialized) {
         // Check setting for OS X 10.8+.
         id value = [[NSUserDefaults standardUserDefaults] objectForKey:@"NSScrollAnimationEnabled"];
         // Check setting for OS X < 10.8.
         if (!value)
             value = [[NSUserDefaults standardUserDefaults] objectForKey:@"AppleScrollAnimationEnabled"];
         if (value)
             animation_enabled = [value boolValue];
         animation_initialized = true;
     }
+    // More temporary logic used until the browser begins to call updateScrollbarsWithNSDefaults method.
     NSString* scrollbar_variant = [[NSUserDefaults standardUserDefaults] objectForKey:@"AppleScrollBarVariant"];
+    ScrollbarButtonsPlacement buttons_placement;
+    if ([scrollbar_variant isEqualToString:@"Single"])
+        buttons_placement = ScrollbarButtonsPlacementSingle;
+    else if ([scrollbar_variant isEqualToString:@"DoubleMin"])
+        buttons_placement = ScrollbarButtonsPlacementDoubleStart;
+    else if ([scrollbar_variant isEqualToString:@"DoubleBoth"])
+        buttons_placement = ScrollbarButtonsPlacementDoubleBoth;
+    else
+        buttons_placement = ScrollbarButtonsPlacementDoubleEnd;
     updateScrollbarsWithNSDefaults(initialButtonDelay, autoscrollButtonDelay,
                                   preferredScrollerStyle, redraw, animation_enabled,
-                                  scrollbar_variant ? [scrollbar_variant UTF8String] : "");
+                                  buttons_placement);
 }
 
 void WebScrollbarTheme::updateScrollbarsWithNSDefaults(
     float initialButtonDelay, float autoscrollButtonDelay,
-    ScrollerStyle preferredScrollerStyle, bool redraw, bool scrollAnimationEnabled, const std::string& buttonPlacement)
+    ScrollerStyle preferredScrollerStyle, bool redraw, bool scrollAnimationEnabled, ScrollbarButtonsPlacement buttonPlacement)
 {
     ScrollbarTheme* theme = ScrollbarTheme::theme();
     if (theme->isMockTheme())
         return;
 
     static_cast<ScrollbarThemeMacCommon*>(ScrollbarTheme::theme())->preferencesChanged(
         initialButtonDelay, autoscrollButtonDelay,
         static_cast<NSScrollerStyle>(preferredScrollerStyle),
         redraw, scrollAnimationEnabled, buttonPlacement);
 }
 
 } // namespace blink