Make updateLayoutAndStyleForPainting() O(N) in terms of frame number in LayoutView::hitTest()

Source/core/layout/LayoutView.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 65 matching lines @@
 
     setPositionState(AbsolutePosition); // to 0,0 :)
 }
 
 LayoutView::~LayoutView()
 {
 }
 
 bool LayoutView::hitTest(HitTestResult& result)
 {
+    // We have to recursively update layout/style here because otherwise, when the hit test recurses
+    // into a child document, it could trigger a layout on the parent document, which can destroy DeprecatedPaintLayer
+    // that are higher up in the call stack, leading to crashes.
+    // Note that Document::updateLayout calls its parent's updateLayout.
+    frameView()->updateLayoutAndStyleForPainting();
+    return hitTestNoLayoutAndStyleUpdate(result);
+}
+
+bool LayoutView::hitTestNoLayoutAndStyleUpdate(HitTestResult& result)
+{
     TRACE_EVENT_BEGIN0("blink,devtools.timeline", "HitTest");
     m_hitTestCount++;
 
     ASSERT(!result.hitTestLocation().isRectBasedTest() || result.hitTestRequest().listBased());
 
-    // We have to recursively update layout/style here because otherwise, when the hit test recurses
-    // into a child document, it could trigger a layout on the parent document, which can destroy DeprecatedPaintLayer
-    // that are higher up in the call stack, leading to crashes.
-    // Note that Document::updateLayout calls its parent's updateLayout.
-    // FIXME: It should be the caller's responsibility to ensure an up-to-date layout.
-    frameView()->updateLayoutAndStyleForPainting();
     commitPendingSelection();
 
     uint64_t domTreeVersion = document().domTreeVersion();
     HitTestResult cacheResult = result;
     bool cacheHit = m_hitTestCache->lookupCachedResult(cacheResult, domTreeVersion);
     bool hitLayer = layer()->hitTest(result);
 
     // FrameView scrollbars are not the same as Layer scrollbars tested by Layer::hitTestOverflowControls,
     // so we need to test FrameView scrollbars separately here. Note that it's important we do this after
     // the hit test above, because that may overwrite the entire HitTestResult when it finds a hit.
@@ skipping 851 matching lines @@
     return viewHeight(IncludeScrollbars) / scale;
 }
 
 void LayoutView::willBeDestroyed()
 {
     LayoutBlockFlow::willBeDestroyed();
     m_compositor.clear();
 }
 
 } // namespace blink