Introduce FlatTreeTraversal:: AncestorsOf()

This patch introduces |FlatTreeTraversal::AncestorsOf()| as |NodeTraversal|.

This patch is a preparation of the patch[1].

Note: The patch[2] introduces |FlatTreeTraversal::InclusiveAncestorsOf()|.

[1] http://crrev.com/c/737981 Introduce TextOffsetMapping to simplify
word/paragraph selection
[2] http://crrev.com/c/742770 Introduce FlatTreeTraversal::InclusiveAncestorsOf

Bug: 778507
Change-Id: I5f76f00c06a4e02b5981600049af11853fa2f60b
Reviewed-on: https://chromium-review.googlesource.com/923443Reviewed-by: Hayato Ito <hayato@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537237}

third_party/WebKit/Source/core/dom/FlatTreeTraversal.h

@@ -127,11 +127,12 @@ class CORE_EXPORT FlatTreeTraversal {
   // Flat tree range helper functions for range based for statement.
   // TODO(dom-team): We should have following functions to match with
   // |NodeTraversal|:
-  //   - AncestorsOf()
   //   - DescendantsOf()
   //   - InclusiveDescendantsOf()
   //   - StartsAt()
   //   - StartsAfter()
+  static TraversalRange<TraversalAncestorsIterator<FlatTreeTraversal>>
+  AncestorsOf(const Node&);
   static TraversalRange<TraversalChildrenIterator<FlatTreeTraversal>>
   ChildrenOf(const Node&);
 
@@ -341,6 +342,11 @@ inline Node* FlatTreeTraversal::TraverseLastChild(const Node& node) {
 }
 
 // TraverseRange<T> implementations
+inline TraversalRange<TraversalAncestorsIterator<FlatTreeTraversal>>
+FlatTreeTraversal::AncestorsOf(const Node& node) {
+  return TraversalRange<TraversalAncestorsIterator<FlatTreeTraversal>>(&node);
+}
+
 inline TraversalRange<TraversalChildrenIterator<FlatTreeTraversal>>
 FlatTreeTraversal::ChildrenOf(const Node& parent) {
   return TraversalRange<TraversalChildrenIterator<FlatTreeTraversal>>(&parent);

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

@@ -320,6 +320,23 @@ TEST_F(FlatTreeTraversalTest, nextSkippingChildren) {
   EXPECT_EQ(*m1, FlatTreeTraversal::PreviousSkippingChildren(*m2));
 }
 
+TEST_F(FlatTreeTraversalTest, AncestorsOf) {
+  SetupDocumentTree("<div><div><div id=sample></div></div></div>");
+  Element* const sample = GetDocument().getElementById("sample");
+
+  HeapVector<Member<Node>> expected_nodes;
+  for (Node* parent = FlatTreeTraversal::Parent(*sample); parent;
+       parent = FlatTreeTraversal::Parent(*parent)) {
+    expected_nodes.push_back(parent);
+  }
+
+  HeapVector<Member<Node>> actual_nodes;
+  for (Node& ancestor : FlatTreeTraversal::AncestorsOf(*sample))
+    actual_nodes.push_back(&ancestor);
+
+  EXPECT_EQ(expected_nodes, actual_nodes);
+}
+
 TEST_F(FlatTreeTraversalTest, InclusiveAncestorsOf) {
   SetupDocumentTree("<div><div><div id=sample></div></div></div>");
   Element* const sample = GetDocument().getElementById("sample");