Aura overlay scrollbars adjust color for dark backgrounds

third_party/WebKit/public/platform/WebThemeEngine.h

Index: third_party/WebKit/public/platform/WebThemeEngine.h
diff --git a/third_party/WebKit/public/platform/WebThemeEngine.h b/third_party/WebKit/public/platform/WebThemeEngine.h
index 55f74b52a08b8399025b4d2a84d24d96e4f84222..9f20c1267e18c8f86a55cfc39f849f191c0d23b0 100644
--- a/third_party/WebKit/public/platform/WebThemeEngine.h
+++ b/third_party/WebKit/public/platform/WebThemeEngine.h
@@ -137,6 +137,13 @@ class WebThemeEngine {
     int valueRectHeight;
   };
 
+  // Extra parameters for Scrollbar, now only for overlay-scrollbar
+  enum ScrollbarOverlayColorTheme {

[bokan, 2016/10/21 16:57:14]

Create a ScrollbarOverlayColorTheme.h file and put this enum in there. Use that
here and in WebScrollbar.h

+    ScrollbarOverlayColorThemeDefault,
+    ScrollbarOverlayColorThemeDark,
+    ScrollbarOverlayColorThemeLight
+  };
+
   union ExtraParams {
     ScrollbarTrackExtraParams scrollbarTrack;
     ButtonExtraParams button;
@@ -145,6 +152,7 @@ class WebThemeEngine {
     SliderExtraParams slider;
     InnerSpinButtonExtraParams innerSpin;
     ProgressBarExtraParams progressBar;
+    ScrollbarOverlayColorTheme scrollbarTheme;

[bokan, 2016/10/21 16:57:14]

Similarly to the NativeTheme::ExtraParams, this isn't a union state. In this
case, thumb probably doesn't specify extra params from Web so please add a
struct ScrollbarThumbExtraParams that has the scrollbarTheme and add
ScrollbarThumbExtraParams to the union.

   };
 
   // Gets the size of the given theme part. For variable sized items