Consider slots as a focus scope

third_party/WebKit/Source/core/dom/shadow/AssignedElementTraversal.cpp

Index: third_party/WebKit/Source/core/dom/shadow/AssignedElementTraversal.cpp
diff --git a/third_party/WebKit/Source/core/dom/shadow/AssignedElementTraversal.cpp b/third_party/WebKit/Source/core/dom/shadow/AssignedElementTraversal.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..7ab0e12e15b879e33b0772b0489cb40197e41f77
--- /dev/null
+++ b/third_party/WebKit/Source/core/dom/shadow/AssignedElementTraversal.cpp
@@ -0,0 +1,80 @@
+// 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/shadow/AssignedElementTraversal.h"
+
+#include "core/dom/Element.h"
+#include "core/dom/ElementTraversal.h"
+#include "core/html/HTMLSlotElement.h"
+
+namespace blink {
+
+HTMLSlotElement* AssignedElementTraversal::slot(const Element& current)
+{
+    if (Element* assignedAncestor = AssignedElementTraversal::assignedAncestor(current)) {
+        return assignedAncestor->assignedSlot();
+    }

[kochi, 2016/03/02 13:26:56]

nit: you can remove {}.

[yuzuchan, 2016/03/03 04:12:42]

Done.

+    return nullptr;
+}
+
+Element* AssignedElementTraversal::assignedAncestor(const Element& current)
+{
+    // assignedAncestor returns an ancestor element of current which is directly assigned to a slot.
+    Element* element = const_cast<Element*>(&current);
+    for (; element; element = element->parentElement()) {
+        if (element->assignedSlot())
+            break;
+    }
+    return element;
+}
+
+Element* AssignedElementTraversal::next(const Element& current)
+{
+    // current.assignedSlot returns a slot only when current is assigned explicitly
+    // if current is directly assigned to a slot, return a descendant of current, which is indirectly assigned to the same slot as current.
+    HTMLSlotElement* slot = current.assignedSlot();
+    WillBeHeapVector<RefPtrWillBeMember<Node>> assignedNodes;
+    if (slot) {
+        if (Element* next = ElementTraversal::next(current, &current))
+            return next;
+        // if not, jump to another tree of assigned elements.
+        assignedNodes = slot->getAssignedNodes();
+    } else {
+        // if current is indirectly assigned to a slot, find a directly-assigned ancestor.
+        Element* assignedAncestor = AssignedElementTraversal::assignedAncestor(current);
+        if (Element* next = ElementTraversal::next(current, assignedAncestor))
+            return next;
+        assignedNodes = AssignedElementTraversal::slot(*assignedAncestor)->getAssignedNodes();

[kochi, 2016/03/02 13:26:56]

nit: I feel like on this line it should be
    slot = AssignedElementTraversal::slot(*assignedAncestor);
and remove line 37 and 42, then after this if-else,
WillBeHeapVector<RefPtrWillbeMember<Node>> assignedNodes =
slot->getAsignedNodes();
?

[yuzuchan, 2016/03/03 04:12:42]

Done.

+    }
+    size_t currentIndex = assignedNodes.find(current);
+    if (currentIndex != kNotFound && currentIndex < assignedNodes.size() - 1)
+        return toElement(assignedNodes[currentIndex + 1]);
+    return nullptr;
+}
+
+Element* AssignedElementTraversal::previous(const Element& current)
+{
+    Element* assignedAncestor = AssignedElementTraversal::assignedAncestor(current);
+    // NodeTraversal within assignedAncestor
+    if (Element* previous = ElementTraversal::previous(current, assignedAncestor))
+        return previous;
+    // if null, jump to previous assigned node's descendant
+    const WillBeHeapVector<RefPtrWillBeMember<Node>> assignedNodes = AssignedElementTraversal::slot(*assignedAncestor)->getAssignedNodes();
+    size_t currentIndex = assignedNodes.reverseFind(current);
+    if (currentIndex != kNotFound && currentIndex > 0) {
+        Node* assignedPrevious = assignedNodes[currentIndex - 1];
+        if (Node* lastChild = assignedPrevious->lastChild())
+            return toElement(lastChild);
+        // if the previous assigned node has no children, return the assigned node itself
+        return toElement(assignedPrevious);
+    }
+    return nullptr;
+}
+
+bool AssignedElementTraversal::isInAssignedScope(const Element& current)
+{
+    return AssignedElementTraversal::assignedAncestor(current);

[kochi, 2016/03/02 13:26:56]

aha, you don't need !! in front of AssingedElementTraversal::... this line.
(because of automatic pointer -> bool conversion)

[yuzuchan, 2016/03/03 04:12:42]

Acknowledged.

+}
+
+} // namespace blink