Adds DevTools commands for forced viewport override.

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 c377422df09bc1fb21aaf8e192674c5931fa241d..9df32b57e394954851af095d482e4441e846fc8c 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -676,6 +676,10 @@ void RenderWidgetCompositor::setViewportSize(
   layer_tree_host_->GetLayerTree()->SetViewportSize(device_viewport_size);
 }
 
+WebSize RenderWidgetCompositor::getViewportSize() const {
+  return layer_tree_host_->GetLayerTree()->device_viewport_size();
+}
+
 WebFloatPoint RenderWidgetCompositor::adjustEventPointForPinchZoom(
     const WebFloatPoint& point) const {
   return point;