Overlay scrollbars flush with window edge

ui/native_theme/native_theme.h

Index: ui/native_theme/native_theme.h
diff --git a/ui/native_theme/native_theme.h b/ui/native_theme/native_theme.h
index 7aa469a50b537f2d293d79f5cbd92bfd7f5c76f8..e334fcd2c84d531b088c630f103b17330b73df2f 100644
--- a/ui/native_theme/native_theme.h
+++ b/ui/native_theme/native_theme.h
@@ -202,6 +202,7 @@ class NATIVE_THEME_EXPORT NativeTheme {
   struct ScrollbarThumbExtraParams {
     bool is_hovering;
     ScrollbarOverlayColorTheme scrollbar_theme;
+    bool isLeftVerticalScrollbar;

[Evan Stade, 2017/03/28 00:01:56]

nit: is_left_vertical_scrollbar

but also, it seems like we should instead be splitting the part into two (one
for left vertical bar and one for right vertical bar), or making this param a
generic rtl parameter.

[chaopeng, 2017/03/28 02:58:40]

Sorry, I don't get this one. Why we need is right vertical scrollbar? We use
IsLeftSideVerticalScrollbar everywhere like this.
https://cs.chromium.org/chromium/src/cc/input/scrollbar.h?q=scrollba&l=26

[Evan Stade, 2017/03/28 03:14:36]

I meant that the Part enum should have different values.

   };
 
   struct SliderExtraParams {