Throttle rendering pipeline for invisible iframes

Source/web/WebViewImpl.cpp

 /*
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 1865 matching lines @@
             mainFrameImpl()->frame()->eventHandler().handleGestureScrollEnd(endScrollEvent);
         }
     }
 
     if (!m_page)
         return;
 
     // FIXME: This should probably be using the local root?
     if (m_page->mainFrame()->isLocalFrame())
         PageWidgetDelegate::animate(*m_page, validFrameTime.lastFrameTimeMonotonic, *m_page->deprecatedLocalMainFrame());
+
+    // HACK: simulate the commit signal for layout tests
+    //Platform::current()->mainThread()->postTask(FROM_HERE, bind(&WebViewImpl::didCommitCompositorFrame, this));
 }
 
 void WebViewImpl::layout()
 {
     TRACE_EVENT0("blink", "WebViewImpl::layout");
     if (!mainFrameImpl())
         return;
 
     PageWidgetDelegate::layout(*m_page, *mainFrameImpl()->frame());
     updateLayerTreeBackgroundColor();
@@ skipping 28 matching lines @@
     ASSERT(!isAcceleratedCompositingActive());
 
     double paintStart = currentTime();
     PageWidgetDelegate::paint(*m_page, canvas, rect, *m_page->deprecatedLocalMainFrame());
     double paintEnd = currentTime();
     double pixelsPerSec = (rect.width * rect.height) / (paintEnd - paintStart);
     Platform::current()->histogramCustomCounts("Renderer4.SoftwarePaintDurationMS", (paintEnd - paintStart) * 1000, 0, 120, 30);
     Platform::current()->histogramCustomCounts("Renderer4.SoftwarePaintMegapixPerSecond", pixelsPerSec / 1000000, 10, 210, 30);
 }
 
+void WebViewImpl::didCommitCompositorFrame()
+{
+    if (!mainFrameImpl() || !mainFrameImpl()->frameView())
+        return;
+    FrameView* view = mainFrameImpl()->frameView();
+    view->updateThrottling();

[ojan, 2015/09/01 19:56:48]

I was picturing that this would be called unconditionally at the end of
FrameView::updateLifecyclePhasesInternal (in the AllPhases branch at the
bottom). So, WebViewImpl doesn't need to know anything about it.

Is there a reason it needs to be here?

[Sami, 2015/09/02 10:46:03]

Yeah, that was my assumption too but the problem is painting happens after
updateLifecyclePhasesInternal(), so we might try to paint a frame that just
became unthrottled but didn't do a lifecycle update. I'm open to suggestion here
-- maybe this callback should be more painting specific or maybe we do a forced
lifecycle update when unthrottling?

[ojan, 2015/09/02 11:33:27]

Ah right. Doing it synchronously in updateLifecyclePhasesInternal doesn't work.
If we want to match what PositionObserver (now IntersectionObserver) is planning
to do, which I think we do if we can, then we'd do a PostTask from inside
updateLifecyclePhasesInternal. esprehn, does this match your intended direction
for the IntersectionObserver implementation?

[dglazkov, 2015/09/03 16:51:28]

I am still a little bit confused, please forgive me. It seems that
DidCommitCompositorFrame originates from the tail end of the
ThreadProxy::BeginMainFrame
(https://code.google.com/p/chromium/codesearch#chromium/src/cc/trees/thread_pr...),
and the call to WebViewImpl::layout (which is here:
https://code.google.com/p/chromium/codesearch#chromium/src/cc/trees/thread_pr...)
is right before it. Is there something interesting that can happen between these
two that would make any difference?

[Sami, 2015/09/03 19:29:09]

I just gave the PostTask approach a try since you were going to do it for
IntersectionObserver anyway. A small problem is that any tasks (e.g., input
handling) might slip between the lifecycle update and the posted task, which
means that we can't rely on being at in a clean lifecycle state once the task
runs. I think throttling updates can be made to work regardless, but do you
think that's gonna be a problem for IntersectionObserver? Would the explicit
commit signal be better?

+}
+
 #if OS(ANDROID)
 void WebViewImpl::paintCompositedDeprecated(WebCanvas* canvas, const WebRect& rect)
 {
     // Note: This method exists on OS(ANDROID) and will hopefully be
     //       removed once the link disambiguation feature renders using
     //       the compositor.
     ASSERT(isAcceleratedCompositingActive());
 
     PageWidgetDelegate::paintIgnoringCompositing(*m_page, canvas, rect, *m_page->deprecatedLocalMainFrame());
 }
@@ skipping 2481 matching lines @@
     if (m_pageColorOverlay)
         m_pageColorOverlay->update();
     if (InspectorOverlayImpl* overlay = inspectorOverlay()) {
         PageOverlay* inspectorPageOverlay = overlay->pageOverlay();
         if (inspectorPageOverlay)
             inspectorPageOverlay->update();
     }
 }
 
 } // namespace blink