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 39eb7da57407540f6ef54a4578f2b3a14f7a0dac..0afaa9b99014b559a74ed6bc41213f76cf37b4e4 100644
--- a/content/browser/renderer_host/render_view_host_impl.cc
+++ b/content/browser/renderer_host/render_view_host_impl.cc
@@ -464,7 +464,7 @@ WebPreferences RenderViewHostImpl::ComputeWebkitPrefs() {
   prefs.inert_visual_viewport =
       command_line.HasSwitch(switches::kInertVisualViewport);
 
-  prefs.use_solid_color_scrollbars = ui::IsOverlayScrollbarEnabled();
+  prefs.use_solid_color_scrollbars = false;
 
   prefs.history_entry_requires_user_gesture =
       command_line.HasSwitch(switches::kHistoryEntryRequiresUserGesture);
@@ -482,6 +482,8 @@ 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.