Intersection Observer first draft

Source/core/dom/IntersectionObserver.cpp

Index: Source/core/dom/IntersectionObserver.cpp
diff --git a/Source/core/dom/IntersectionObserver.cpp b/Source/core/dom/IntersectionObserver.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..63912b2cc10a45b2ba47140ae5031c3eb6ba8c3f
--- /dev/null
+++ b/Source/core/dom/IntersectionObserver.cpp
@@ -0,0 +1,102 @@
+// Copyright 2015 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 "config.h"
+#include "core/dom/IntersectionObserver.h"
+
+#include "bindings/core/v8/ExceptionState.h"
+#include "core/dom/Document.h"
+#include "core/dom/ExceptionCode.h"
+#include "core/dom/ExecutionContext.h"
+#include "core/dom/IntersectionObserverCallback.h"
+#include "core/dom/IntersectionObserverEntry.h"
+#include "core/dom/IntersectionObserverInit.h"
+#include "platform/Timer.h"
+#include "wtf/MainThread.h"
+#include <algorithm>
+
+namespace blink {
+
+PassRefPtrWillBeRawPtr<IntersectionObserver> IntersectionObserver::create(Document* document, PassOwnPtrWillBeRawPtr<IntersectionObserverCallback> callback)
+{
+    ASSERT(isMainThread());
+    return adoptRefWillBeNoop(new IntersectionObserver(document, callback));
+}
+
+IntersectionObserver::IntersectionObserver(Document* document, PassOwnPtrWillBeRawPtr<IntersectionObserverCallback> callback)
+    : m_callback(callback)
+    , m_document(document)
+{
+}
+
+IntersectionObserver::~IntersectionObserver()
+{
+}
+
+void IntersectionObserver::observe(Element* target, const IntersectionObserverInit& observerInit, ExceptionState& exceptionState)
+{
+    if (!m_document) {
+        exceptionState.throwTypeError("Window may be destroyed? Document is invalid.");
+        return;
+    }
+    if (!target) {
+        exceptionState.throwTypeError("Invalid observation target (null).");
+        return;
+    }
+
+    target->registerIntersectionObserver(this);
+    m_targets.append(target);
+}
+
+void IntersectionObserver::disconnect()
+{
+    m_entries.clear();
+    for (auto target : m_targets) {
+        if (target)

[ojan, 2015/09/21 03:49:09]

How can target be null?

[MikeB, 2015/09/24 19:04:03]

RefPtrWillBeWeakMember will become WeakMember when Oilpan is enabled. In that
case, it can become null if the referenced object is GC'ed.

+            target->unregisterIntersectionObserver(this);
+    }
+    m_targets.clear();
+}
+
+IntersectionObserverEntryVector IntersectionObserver::takeRecords()
+{
+    IntersectionObserverEntryVector entries;
+    entries.swap(m_entries);
+    return entries;
+}
+
+void IntersectionObserver::enqueueIntersectionObserverEntry(PassRefPtrWillBeRawPtr<IntersectionObserverEntry> entry)
+{
+    ASSERT(isMainThread());
+    m_entries.append(entry);
+    if (m_document)
+        m_document->activateIntersectionObserver(*this);
+}
+
+bool IntersectionObserver::shouldBeSuspended() const

[ojan, 2015/09/21 03:49:09]

I see that MutationObservers are also ActiveDOMObjects, but it's not clear to me
why they are and whether IntersectionObserver should be also. Adam?

+{
+    return m_callback->executionContext() && m_callback->executionContext()->activeDOMObjectsAreSuspended();
+}
+
+void IntersectionObserver::deliver()
+{
+    ASSERT(!shouldBeSuspended());
+
+    if (m_entries.isEmpty())
+        return;
+
+    IntersectionObserverEntryVector entries;
+    entries.swap(m_entries);
+    m_callback->handleEvent(entries, this);
+}
+
+DEFINE_TRACE(IntersectionObserver)
+{
+    visitor->trace(m_callback);
+    visitor->trace(m_document);
+    visitor->trace(m_entries);
+    visitor->trace(m_targets);
+}
+
+} // namespace blink