Add more specific metrics for main thread scrolling reasons

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.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@gmail.com>
@@ skipping 88 matching lines @@
       m_needsCompositedScrolling(false),
       m_rebuildHorizontalScrollbarLayer(false),
       m_rebuildVerticalScrollbarLayer(false),
       m_needsScrollOffsetClamp(false),
       m_needsRelayout(false),
       m_hadHorizontalScrollbarBeforeRelayout(false),
       m_hadVerticalScrollbarBeforeRelayout(false),
       m_scrollbarManager(*this),
       m_scrollCorner(nullptr),
       m_resizer(nullptr),
-      m_scrollAnchor(this)
+      m_scrollAnchor(this),
+      m_reasons(0)
 #if DCHECK_IS_ON()
       ,
       m_hasBeenDisposed(false)
 #endif
 {
   Node* node = box().node();
   if (node && node->isElementNode()) {
     // We save and restore only the scrollOffset as the other scroll values are
     // recalculated.
     Element* element = toElement(node);
@@ skipping 17 matching lines @@
       frame->eventHandler().resizeScrollableAreaDestroyed();
   }
 
   if (LocalFrame* frame = box().frame()) {
     if (FrameView* frameView = frame->view()) {
       frameView->removeScrollableArea(this);
       frameView->removeAnimatingScrollableArea(this);
     }
   }
 
+  removeStyleRelatedMainThreadScrollingReasons();
+
   if (ScrollingCoordinator* scrollingCoordinator = getScrollingCoordinator())
     scrollingCoordinator->willDestroyScrollableArea(this);
 
   if (!box().documentBeingDestroyed()) {
     Node* node = box().node();
     // FIXME: Make setSavedLayerScrollOffset take DoubleSize. crbug.com/414283.
     if (node && node->isElementNode())
       toElement(node)->setSavedLayerScrollOffset(m_scrollOffset);
   }
 
@@ skipping 1557 matching lines @@
 }
 
 bool PaintLayerScrollableArea::shouldScrollOnMainThread() const {
   if (LocalFrame* frame = box().frame()) {
     if (frame->view()->mainThreadScrollingReasons())
       return true;
   }
   return ScrollableArea::shouldScrollOnMainThread();
 }
 
-static bool layerNeedsCompositedScrolling(
-    PaintLayerScrollableArea::LCDTextMode mode,
+bool PaintLayerScrollableArea::layerNeedsCompositedScrolling(
+    const LCDTextMode mode,
     const PaintLayer* layer) {
   if (!layer->scrollsOverflow())
     return false;
 
   Node* node = layer->enclosingNode();
   if (node && node->isElementNode() &&
       (toElement(node)->compositorMutableProperties() &
        (CompositorMutableProperty::kScrollTop |
         CompositorMutableProperty::kScrollLeft)))
     return true;
 
   // TODO(flackr): Allow integer transforms as long as all of the ancestor
   // transforms are also integer.
   bool backgroundSupportsLCDText =
       RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled() &&
       layer->layoutObject()->style()->isStackingContext() &&
       layer->backgroundPaintLocation() & BackgroundPaintInScrollingContents &&
       layer->backgroundIsKnownToBeOpaqueInRect(
           toLayoutBox(layer->layoutObject())->paddingBoxRect()) &&
       !layer->compositesWithTransform() && !layer->compositesWithOpacity();
+
   if (mode == PaintLayerScrollableArea::ConsiderLCDText &&
       !layer->compositor()->preferCompositingToLCDTextEnabled() &&
-      !backgroundSupportsLCDText)
+      !backgroundSupportsLCDText) {
+    if (layer->compositesWithOpacity()) {
+      addStyleRelatedMainThreadScrollingReasons(

[bokan, 2016/12/20 19:35:53]

This still has the issue I brought up in the last patchset. There's only one
place this method is called from - updateNeedsCompositedScrolling which is only
a few lines long. Just inline this entire method in there.

[yigu, 2016/12/20 19:59:31]

Renamed the method to computeNeedsCompositedScrolling to be clear.

+          MainThreadScrollingReason::kHasOpacity);
+    }
     return false;
+  }
 
   // TODO(schenney) Tests fail if we do not also exclude
   // layer->layoutObject()->style()->hasBorderDecoration() (missing background
   // behind dashed borders). Resolve this case, or not, and update this check
   // with the results.
   return !(layer->size().isEmpty() || layer->hasDescendantWithClipPath() ||
            layer->hasAncestorWithClipPath() ||
            layer->layoutObject()->style()->hasBorderRadius());
 }
 
+void PaintLayerScrollableArea::addStyleRelatedMainThreadScrollingReasons(
+    const uint32_t reason) {
+  LocalFrame* frame = box().frame();
+  if (!frame)
+    return;
+  FrameView* frameView = frame->view();
+  if (!frameView)
+    return;
+
+  frameView->adjustStyleRelatedMainThreadScrollingReasons(reason, true);
+
+  setMainThreadScrollingReason(reason);
+}
+
+void PaintLayerScrollableArea::removeStyleRelatedMainThreadScrollingReasons() {
+  LocalFrame* frame = box().frame();
+  if (!frame)
+    return;
+  FrameView* frameView = frame->view();
+  if (!frameView)
+    return;
+
+  // Decrese the number of layers that have any main thread
+  // scrolling reasons stored in FrameView
+  for (uint32_t i = 0;
+       i < MainThreadScrollingReason::kMainThreadScrollingReasonCount; ++i) {
+    uint32_t reason = 1 << i;
+    if (hasMainThreadScrollingReason(reason)) {
+      resetMainThreadScrollingReason(reason);
+      frameView->adjustStyleRelatedMainThreadScrollingReasons(reason, false);
+    }
+  }
+}
+
 void PaintLayerScrollableArea::updateNeedsCompositedScrolling(
     LCDTextMode mode) {
+  // Clear all style related main thread scrolling reasons, if any,
+  // before calling layerNeedsCompositedScrolling
+  removeStyleRelatedMainThreadScrollingReasons();
   const bool needsCompositedScrolling =
       layerNeedsCompositedScrolling(mode, layer());
+
   if (static_cast<bool>(m_needsCompositedScrolling) !=
       needsCompositedScrolling) {
     m_needsCompositedScrolling = needsCompositedScrolling;
     layer()->didUpdateNeedsCompositedScrolling();
   }
 }
 
 void PaintLayerScrollableArea::setTopmostScrollChild(PaintLayer* scrollChild) {
   // We only want to track the topmost scroll child for scrollable areas with
   // overlay scrollbars.
@@ skipping 252 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollOffsetClampScope::
     clampScrollableAreas() {
   for (auto& scrollableArea : *s_needsClamp)
     scrollableArea->clampScrollOffsetAfterOverflowChange();
   delete s_needsClamp;
   s_needsClamp = nullptr;
 }
 
 }  // namespace blink