Add API to send NSUserDefault values over IPC, while preserving current behavior

Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm

Index: Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm
diff --git a/Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm b/Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm
index b2283ae770f87674f9c4af8735b12355dc262c11..1aaec1b8fd19ac1132eb0371d72279bca310af7d 100644
--- a/Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm
+++ b/Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm
@@ -58,18 +58,16 @@ static int cOuterButtonOverlap = 2;
 
 static ScrollbarButtonsPlacement gButtonPlacement = ScrollbarButtonsDoubleEnd;
 
-void ScrollbarThemeMacNonOverlayAPI::updateButtonPlacement()
+void ScrollbarThemeMacNonOverlayAPI::updateButtonPlacement(const std::string& buttonPlacement)
 {
-    NSString *buttonPlacement = [[NSUserDefaults standardUserDefaults] objectForKey:@"AppleScrollBarVariant"];
-    if ([buttonPlacement isEqualToString:@"Single"])
+    if (buttonPlacement == "Single")
         gButtonPlacement = ScrollbarButtonsSingle;
-    else if ([buttonPlacement isEqualToString:@"DoubleMin"])
+    else if (buttonPlacement == "DoubleMin")
         gButtonPlacement = ScrollbarButtonsDoubleStart;
-    else if ([buttonPlacement isEqualToString:@"DoubleBoth"])
+    else if (buttonPlacement == "DoubleBoth")
         gButtonPlacement = ScrollbarButtonsDoubleBoth;
-    else {
+    else
         gButtonPlacement = ScrollbarButtonsDoubleEnd;
-    }
 }
 
 // Override ScrollbarThemeMacCommon::paint() to add support for the following: