Allow local root FrameView to be throttled

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 2350 matching lines @@
 
 void FrameView::updateLifecyclePhasesInternal(LifeCycleUpdateOption phases)
 {
     // This must be called from the root frame, since it recurses down, not up.
     // Otherwise the lifecycles of the frames might be out of sync.
     ASSERT(m_frame->isLocalRoot());
 
     // Updating layout can run script, which can tear down the FrameView.
     RefPtrWillBeRawPtr<FrameView> protector(this);
 
+    if (shouldThrottleRendering()) {
+        updateViewportIntersectionsForSubtree();

[ojan, 2015/12/01 01:11:05]

Do we need to update the intersections for the subtree if we're throttled?

As I look more closely, do we need to update the intersections in the
OnlyUpToLayoutClean early return either?

It seems to me that in both cases we only need to do this if we're running the
whole pipeline unthrottled (for this subtree). I'm probably missing some
complication though.

The early return here makes sense to me though.

[Sami, 2015/12/04 18:39:53]

We need to update the subtree in both cases because otherwise we could end up in
a situation where the root becomes throttled but the whole subtree isn't also
marked throttled. This leads to failing lifecycle asserts because the subtree's
lifecycle is in some random state (because the root was throttled) but the
throttled flag isn't set.

N.B. updateViewportIntersectionsForSubtree() has early-outs so in the common
case it won't do much work.

+        return;
+    }
+
     updateStyleAndLayoutIfNeededRecursive();
     ASSERT(lifecycle().state() >= DocumentLifecycle::LayoutClean);
 
     if (phases == OnlyUpToLayoutClean) {
         updateViewportIntersectionsForSubtree();
         return;
     }
 
     if (LayoutView* view = layoutView()) {
         TRACE_EVENT1("devtools.timeline", "UpdateLayerTree", "data", InspectorUpdateLayerTreeEvent::data(m_frame.get()));
@@ skipping 1596 matching lines @@
     return m_hiddenForThrottling && m_crossOriginForThrottling;
 }
 
 LayoutBox& FrameView::boxForScrollControlPaintInvalidation() const
 {
     ASSERT(layoutView());
     return *layoutView();
 }
 
 } // namespace blink