Change Aura overlay scrollbars from solid color to painted scrollbars.

third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp

Index: third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp
index 655c9203cf97f5ad111eb4dff98f233ba3baa4db..6d213bed316a255435be846e8e016c116a4cfec2 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp
@@ -126,12 +126,20 @@ PartPaintingParams buttonPartPaintingParams(
   return PartPaintingParams(paintPart, state);
 }
 
+static int getScrollbarThickness() {
+  return Platform::current()
+      ->themeEngine()
+      ->getSize(WebThemeEngine::PartScrollbarVerticalThumb)
+      .width;
+}
+
 }  // namespace
 
 ScrollbarTheme& ScrollbarTheme::nativeTheme() {
   if (RuntimeEnabledFeatures::overlayScrollbarsEnabled()) {
-    DEFINE_STATIC_LOCAL(ScrollbarThemeOverlay, theme,
-                        (10, 0, ScrollbarThemeOverlay::AllowHitTest));
+    DEFINE_STATIC_LOCAL(
+        ScrollbarThemeOverlay, theme,
+        (getScrollbarThickness(), 0, ScrollbarThemeOverlay::AllowHitTest));
     return theme;
   }