IntersectionObserver: use edge-inclusive geometry for intersections.

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/dom/IntersectionObserver.h"
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "core/css/parser/CSSParserTokenRange.h"
 #include "core/css/parser/CSSTokenizer.h"
 #include "core/dom/ExceptionCode.h"
@@ skipping 272 matching lines @@
 
     rect.setX(rect.x() - leftMargin);
     rect.setWidth(rect.width() + leftMargin + rightMargin);
     rect.setY(rect.y() - topMargin);
     rect.setHeight(rect.height() + topMargin + bottomMargin);
 }
 
 unsigned IntersectionObserver::firstThresholdGreaterThan(float ratio) const
 {
     unsigned result = 0;
-
-    // Special handling for zero threshold, which means "any non-zero number of pixels."
-    // If the ratio is zero, then it should be treated as smaller than any threshold,
-    // even a zero threshold.
-    if (!ratio)
-        return 0;
-
     while (result < m_thresholds.size() && m_thresholds[result] <= ratio)
         ++result;
     return result;
 }
 
 void IntersectionObserver::deliver()
 {
 
     if (m_entries.isEmpty())
         return;
 
     HeapVector<Member<IntersectionObserverEntry>> entries;
     entries.swap(m_entries);
     m_callback->handleEvent(entries, *this);
 }
 
 DEFINE_TRACE(IntersectionObserver)
 {
 #if ENABLE(OILPAN)
     visitor->template registerWeakMembers<IntersectionObserver, &IntersectionObserver::clearWeakMembers>(this);
 #endif
     visitor->trace(m_callback);
     visitor->trace(m_observations);
     visitor->trace(m_entries);
 }
 
 } // namespace blink