Split NativeThemeAura into Overlay and NonOverlay versions.

third_party/WebKit/public/web/WebRuntimeFeatures.h

Index: third_party/WebKit/public/web/WebRuntimeFeatures.h
diff --git a/third_party/WebKit/public/web/WebRuntimeFeatures.h b/third_party/WebKit/public/web/WebRuntimeFeatures.h
index 2ba4161b4282c9655990761e19998b1c2505b3f9..0b3506ee970bde3e41b98417f1ec1da81f4227bc 100644
--- a/third_party/WebKit/public/web/WebRuntimeFeatures.h
+++ b/third_party/WebKit/public/web/WebRuntimeFeatures.h
@@ -68,6 +68,9 @@ class WebRuntimeFeatures {
   BLINK_EXPORT static void enableOriginTrials(bool);
   BLINK_EXPORT static bool isOriginTrialsEnabled();
 
+  BLINK_EXPORT static void enableOverlayScrollbars(bool);
+  BLINK_EXPORT static bool isOverlayScrollbarsEnabled();
+
   BLINK_EXPORT static void enableAccelerated2dCanvas(bool);
   BLINK_EXPORT static void enableAudioOutputDevices(bool);
   BLINK_EXPORT static void enableCanvas2dImageChromium(bool);
@@ -92,7 +95,6 @@ class WebRuntimeFeatures {
   BLINK_EXPORT static void enableNotificationConstructor(bool);
   BLINK_EXPORT static void enableNotifications(bool);
   BLINK_EXPORT static void enableOrientationEvent(bool);
-  BLINK_EXPORT static void enableOverlayScrollbars(bool);
   BLINK_EXPORT static void enablePagePopup(bool);
   BLINK_EXPORT static void enableParseHTMLOnMainThread(bool);
   BLINK_EXPORT static void enablePassiveDocumentEventListeners(bool);