New UMA stats for stacking container opt-in measurements.

Source/core/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 116 matching lines @@
     : m_inResizeMode(false)
     , m_scrollDimensionsDirty(true)
     , m_normalFlowListDirty(true)
     , m_hasSelfPaintingLayerDescendant(false)
     , m_hasSelfPaintingLayerDescendantDirty(false)
     , m_hasOutOfFlowPositionedDescendant(false)
     , m_hasOutOfFlowPositionedDescendantDirty(true)
     , m_hasUnclippedDescendant(false)
     , m_isUnclippedDescendant(false)
     , m_needsCompositedScrolling(false)
+    , m_needsCompositedScrollingHasBeenRecorded(false)
+    , m_willUseCompositedScrollingHasBeenRecorded(false)
+    , m_isScrollableAreaHasBeenRecorded(false)
     , m_canBePromotedToStackingContainer(false)
     , m_canBePromotedToStackingContainerDirty(true)
     , m_isRootLayer(renderer->isRenderView())
     , m_usedTransparency(false)
     , m_paintingInsideReflection(false)
     , m_inOverflowRelayout(false)
     , m_repaintStatus(NeedsNormalRepaint)
     , m_visibleContentStatusDirty(true)
     , m_hasVisibleContent(false)
     , m_visibleDescendantStatusDirty(false)
@@ skipping 1930 matching lines @@
     // We gather a boolean value for use with Google UMA histograms to
     // quantify the actual effects of a set of patches attempting to
     // relax composited scrolling requirements, thereby increasing the
     // number of composited overflow divs.
     if (acceleratedCompositingForOverflowScrollEnabled())
         HistogramSupport::histogramEnumeration("Renderer.NeedsCompositedScrolling", needsCompositedScrolling, 2);
 
     setNeedsCompositedScrolling(needsCompositedScrolling);
 }
 
+enum CompositedScrollingHistogramBuckets {
+    IsScrollableAreaBucket = 0,
+    NeedsToBeStackingContainerBucket = 1,
+    WillUseCompositedScrollingBucket = 2
+};
+
 void RenderLayer::setNeedsCompositedScrolling(bool needsCompositedScrolling)
 {
     if (m_needsCompositedScrolling == needsCompositedScrolling)
         return;
 
+    // Count the total number of RenderLayers which need to be stacking
+    // containers some point. This should be recorded at most once per
+    // RenderLayer, so we check m_needsCompositedScrollingHasBeenRecorded.
+    if (acceleratedCompositingForOverflowScrollEnabled() && !m_needsCompositedScrollingHasBeenRecorded) {
+        HistogramSupport::histogramEnumeration("Renderer.CompositedScrolling", NeedsToBeStackingContainerBucket, 3);

[Alexei Svitkine (slow), 2013/09/04 15:21:19]

Nit: Instead of hardcoding 3 for the last param at all the callsites, add it to
the enum - naming it something like CompositedScrollingHistogramMax.

[hartmanng, 2013/09/04 15:48:56]

Done.

+        m_needsCompositedScrollingHasBeenRecorded = true;
+    }
+
+    // Count the total number of RenderLayers which need composited scrolling at
+    // some point. This should be recorded at most once per RenderLayer, so we
+    // check m_willUseCompositedScrollingHasBeenRecorded.
+    //
+    // FIXME: Currently, this computes the exact same value as the above.
+    // However, it will soon be expanded to cover more than just stacking
+    // containers (see crbug.com/249354). When this happens, we should see a
+    // spike in "WillUseCompositedScrolling", while "NeedsToBeStackingContainer"
+    // will remain relatively static.
+    if (acceleratedCompositingForOverflowScrollEnabled() && !m_willUseCompositedScrollingHasBeenRecorded) {
+        HistogramSupport::histogramEnumeration("Renderer.CompositedScrolling", WillUseCompositedScrollingBucket, 3);
+        m_willUseCompositedScrollingHasBeenRecorded = true;
+    }
+
     m_needsCompositedScrolling = needsCompositedScrolling;
 
     // Note, the z-order lists may need to be rebuilt, but our code guarantees
     // that we have not affected stacking, so we will not dirty
     // m_canBePromotedToStackingContainer for either us or our stacking context
     // or container.
     didUpdateNeedsCompositedScrolling();
 }
 
 void RenderLayer::setForceNeedsCompositedScrolling(RenderLayer::ForceNeedsCompositedScrollingMode mode)
@@ skipping 4076 matching lines @@
 
     FrameView* frameView = frame->view();
     if (!frameView)
         return;
 
     bool isVisibleToHitTest = renderer()->visibleToHitTesting();
     if (HTMLFrameOwnerElement* owner = frame->ownerElement())
         isVisibleToHitTest &= owner->renderer() && owner->renderer()->visibleToHitTesting();
 
     if (hasOverflow && isVisibleToHitTest) {
-        if (frameView->addScrollableArea(scrollableArea()))
+        if (frameView->addScrollableArea(scrollableArea())) {
             compositor()->setNeedsUpdateCompositingRequirementsState();
+
+            // Count the total number of RenderLayers that are scrollable areas for
+            // any period. We only want to record this at most once per RenderLayer.
+            if (!m_isScrollableAreaHasBeenRecorded) {
+                HistogramSupport::histogramEnumeration("Renderer.CompositedScrolling", IsScrollableAreaBucket, 3);
+                m_isScrollableAreaHasBeenRecorded = true;
+            }
+        }
     } else {
         if (frameView->removeScrollableArea(scrollableArea()))
             setNeedsCompositedScrolling(false);
     }
 }
 
 void RenderLayer::updateScrollCornerStyle()
 {
     RenderObject* actualRenderer = rendererForScrollbar(renderer());
     RefPtr<RenderStyle> corner = renderer()->hasOverflowClip() ? actualRenderer->getUncachedPseudoStyle(PseudoStyleRequest(SCROLLBAR_CORNER), actualRenderer->style()) : PassRefPtr<RenderStyle>(0);
@@ skipping 273 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif