Clean compositing inputs for location APIs for sticky-affected elements.

third_party/WebKit/Source/core/dom/Document.cpp

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index 6b21cdae68acc65b6f96dae48c8b02839a9f62cb..6166a2fd1112183b2ac8c3db05b44616026c04ef 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -2346,6 +2346,30 @@ PassRefPtr<ComputedStyle> Document::StyleForPage(int page_index) {
   return EnsureStyleResolver().StyleForPage(page_index);
 }
 
+void Document::EnsureLifecycleValidForLocationAPIsForNode(const Node* node) {
+  DCHECK(node);
+  if (!node->InActiveDocument())
+    return;
+
+  // For all nodes we must have up-to-date style and have performed layout to do
+  // any location-based calculation.
+  UpdateStyleAndLayoutIgnorePendingStylesheets();
+
+  // The location of elements that are position: sticky is not known until
+  // compositing inputs are cleaned. Therefore, for any elements that are either
+  // sticky or are in a sticky sub-tree (e.g. are affected by a sticky element),
+  // we need to also clean compositing inputs.
+  if (UNLIKELY(View() && node->GetLayoutObject() &&

[fs, 2017/05/01 21:19:34]

Nit: Did you see any effect of the UNLIKELY here? Considering that only the last
part of the expression is "unlikely", and there's no else it seems it becomes a
matter of some I$ misses (or not.) (And AFAIU we shouldn't be sprinkling
UNLIKELY unless they matter - and they don't even do anything on Windows last I
checked...)

[smcgruer, 2017/05/02 15:25:41]

I did not, it was mostly speculative. Removed.

+               node->GetLayoutObject()->Style()->IsInStickySubtree())) {

[fs, 2017/05/01 21:19:34]

Nit: StyleRef().

[smcgruer, 2017/05/02 15:25:41]

Done.

+    if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
+      // In SPv2, compositing inputs are cleaned as part of PrePaint.
+      View()->UpdateAllLifecyclePhasesExceptPaint();
+    } else {
+      View()->UpdateLifecycleToCompositingInputsClean();
+    }
+  }
+}
+
 bool Document::IsPageBoxVisible(int page_index) {
   return StyleForPage(page_index)->Visibility() !=
          EVisibility::kHidden;  // display property doesn't apply to @page.