First draft to enable turning off compositor for unit tests.

views/widget/widget.cc

Index: views/widget/widget.cc
diff --git a/views/widget/widget.cc b/views/widget/widget.cc
index e2b2202d5836a8680eff2f62a85bc46f267a50ed..368efca3be596b1d7ef83a2c0c94f3dbd4a32a03 100644
--- a/views/widget/widget.cc
+++ b/views/widget/widget.cc
@@ -634,7 +634,8 @@ void Widget::EnsureCompositor() {
   // TODO(sad): If there is a parent Widget, then use the same compositor
   //            instead of creating a new one here.
   gfx::AcceleratedWidget widget = native_widget_->GetAcceleratedWidget();
-  if (widget != gfx::kNullAcceleratedWidget)
+  if (widget != gfx::kNullAcceleratedWidget &&
+                View::get_use_acceleration_when_possible())
     compositor_ = ui::Compositor::Create(widget);
 }