aura: Remove old GL paths from RenderWidgetHostViewAura.

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index 5f19a2f9466bed9021a04e66897dac5a2f8058ed..55a570b13793edbbd3378df4110210b8f82b659a 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -930,7 +930,11 @@ scoped_ptr<cc::OutputSurface> RenderWidget::CreateOutputSurface(bool fallback) {
             scoped_ptr<cc::SoftwareOutputDevice>()));
   }
   if (command_line.HasSwitch(cc::switches::kCompositeToMailbox)) {
-    DCHECK(is_threaded_compositing_enabled_);
+    // Composite-to-mailbox is currently used for layout tests in order to cause
+    // them to draw inside in the renderer to do the readback there. This should
+    // no longer be the case when crbug.com/311404 is fixed.
+    DCHECK(is_threaded_compositing_enabled_ ||
+           RenderThreadImpl::current()->layout_test_mode());
     cc::ResourceFormat format = cc::RGBA_8888;
 #if defined(OS_ANDROID)
     if (base::android::SysUtils::IsLowEndDevice())