Added experiment for changing viewport scroll ordering.

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index abc113929c2b8f9cf38e7b7c8bca0e7330b3ffd8..51cc1c9674d3c709f0a2e7151696d654da462e66 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -354,6 +354,9 @@ void RenderWidgetCompositor::Initialize() {
         &settings.initial_debug_state.slow_down_raster_scale_factor);
   }
 
+  settings.viewport_scroll_order_experiment =
+      cmd->HasSwitch(switches::kEnableViewportScrollOrderExperiment);
+
   if (cmd->HasSwitch(cc::switches::kMaxUnusedResourceMemoryUsagePercentage)) {
     int max_unused_resource_memory_percentage;
     if (GetSwitchValueAsInt(