Fix scrollbar buttons on ChromeOS.

ui/native_theme/native_theme_aura.cc

Index: ui/native_theme/native_theme_aura.cc
diff --git a/ui/native_theme/native_theme_aura.cc b/ui/native_theme/native_theme_aura.cc
index 74edcd558c8bb44cc6621c3f100e4a6b58e3f93a..248db953617f2a8d4011e5de20b9b067e53c1af4 100644
--- a/ui/native_theme/native_theme_aura.cc
+++ b/ui/native_theme/native_theme_aura.cc
@@ -80,12 +80,16 @@ NativeThemeAura* NativeThemeAura::instance() {
 }
 #endif
 
-NativeThemeAura::NativeThemeAura() {
-  // We don't draw scrollbar buttons.
+bool NativeThemeAura::HasScrollbarButtons() const {
 #if defined(OS_CHROMEOS)
-  set_scrollbar_button_length(0);

[Evan Stade, 2016/05/24 22:03:54]

I still don't understand why you're changing this

+  // We don't draw scrollbar buttons.
+  return false;
+#else
+  return NativeTheme::HasScrollbarButtons();
 #endif
+}
 
+NativeThemeAura::NativeThemeAura() {
   // Images and alphas declarations assume the following order.
   static_assert(kDisabled == 0, "states unexpectedly changed");
   static_assert(kHovered == 1, "states unexpectedly changed");
@@ -216,8 +220,7 @@ void NativeThemeAura::PaintScrollbarThumbStateTransition(
     // If there are no scrollbuttons then provide some padding so that the thumb
     // doesn't touch the top of the track.
     const int kThumbPadding = 2;
-    const int extra_padding =
-        (scrollbar_button_length() == 0) ? kThumbPadding : 0;
+    const int extra_padding = HasScrollbarButtons() ? 0 : kThumbPadding;
     if (part == NativeTheme::kScrollbarVerticalThumb)
       thumb_rect.Inset(kThumbPadding, extra_padding);
     else