Slimming Paint phase 2 compositing algorithm plumbing

Source/core/layout/LayoutTestHelper.h

Index: Source/core/layout/LayoutTestHelper.h
diff --git a/Source/core/layout/LayoutTestHelper.h b/Source/core/layout/LayoutTestHelper.h
index 20cff2ed544a130301543cd3fb6ddb2f1c4557c9..876ca996cd7c10aa46d63a50d53d4f70426e2d68 100644
--- a/Source/core/layout/LayoutTestHelper.h
+++ b/Source/core/layout/LayoutTestHelper.h
@@ -21,12 +21,14 @@ protected:
 
     Document& document() const { return m_pageHolder->document(); }
 
+    // Both sets the inner html and runs the document lifecycle.
     void setBodyInnerHTML(const String& htmlContent)
     {
         document().body()->setInnerHTML(htmlContent, ASSERT_NO_EXCEPTION);
         document().view()->updateAllLifecyclePhases();
     }
 
+    // Both enables compositing and runs the document lifecycle.
     void enableCompositing()
     {
         m_pageHolder->page().settings().setAcceleratedCompositingEnabled(true);