Initial ResizeObserver implementation

third_party/WebKit/Source/core/observer/ResizeObserverEntry.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/observer/ResizeObserverEntry.h"
+
+#include "core/dom/ClientRect.h"
+#include "core/dom/DOMRectReadOnly.h"
+#include "core/dom/Element.h"
+#include "core/layout/LayoutBox.h"
+
+namespace blink {
+
+class ResizeObservation;
+
+ResizeObserverEntry::ResizeObserverEntry(Element* target)
+    : m_target(target)
+{
+    if (!m_target)
+        return;
+    LayoutBox* layout = m_target->layoutBox();
+    if (!layout) {
+        m_contentRect = ClientRect::create(IntRect(0, 0, 0, 0));
+    } else {
+        m_contentRect = ClientRect::create(FloatRect(
+            layout->paddingLeft(), layout->paddingTop(),

[eae, 2016/07/13 23:39:47]

Shouldn't the location include borderLeft and borderTop? contentWidth explicitly
subtracts the borders (as well as the paddings).

If so you can use ClientRect::create(FloatRect(layout->contentBoxRect()));

[atotic1, 2016/07/15 01:43:17]

Location does not include borderLeft/Top. See discussion at
https://github.com/WICG/ResizeObserver/issues/6

+            layout->contentWidth(), layout->contentHeight()));
+    }
+}
+
+LayoutSize ResizeObserverEntry::contentSize() const
+{
+    return LayoutSize(m_contentRect->width(), m_contentRect->height());
+}
+
+DEFINE_TRACE(ResizeObserverEntry)
+{
+    visitor->trace(m_target);
+    visitor->trace(m_contentRect);
+}
+
+} // namespace blink