Change Aura overlay scrollbars from solid color to painted scrollbars.

content/browser/renderer_host/render_view_host_impl.cc

Index: content/browser/renderer_host/render_view_host_impl.cc
diff --git a/content/browser/renderer_host/render_view_host_impl.cc b/content/browser/renderer_host/render_view_host_impl.cc
index 95852d6da5c6354d74e723cc5ef32b5a822d4fb5..3142f2908207f28f8ce9a0919dee3b9ce53051b5 100644
--- a/content/browser/renderer_host/render_view_host_impl.cc
+++ b/content/browser/renderer_host/render_view_host_impl.cc
@@ -476,7 +476,7 @@ WebPreferences RenderViewHostImpl::ComputeWebkitPrefs() {
       command_line.HasSwitch(switches::kInertVisualViewport);
 
   prefs.pinch_overlay_scrollbar_thickness = 10;
-  prefs.use_solid_color_scrollbars = ui::IsOverlayScrollbarEnabled();
+  prefs.use_solid_color_scrollbars = false;
 
   prefs.history_entry_requires_user_gesture =
       command_line.HasSwitch(switches::kHistoryEntryRequiresUserGesture);
@@ -494,6 +494,8 @@ WebPreferences RenderViewHostImpl::ComputeWebkitPrefs() {
       base::FeatureList::IsEnabled(features::kAutoplayMutedVideos);
 
   prefs.progress_bar_completion = GetProgressBarCompletionPolicy();
+
+  prefs.use_solid_color_scrollbars = true;
 #endif
 
   // Handle autoplay gesture override experiment.