Utilize Position::FirstPositionInNode()

This patch utilizes |Position::FirstPositionInNode()| instead of
constructor with |PositionAnchorType::kBeforeChildren| to reduce source
code size and preparation of getting rid of |kBeforeChildren|.

Bug: 592887
Change-Id: I66640fe772d506965f901326b39604dd83e9d408
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2556733
Commit-Queue: Koji Ishii <kojii@chromium.org>
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830871}

third_party/blink/renderer/core/editing/frame_caret_test.cc

@@ -92,8 +92,7 @@ TEST_F(FrameCaretTest, ShouldNotBlinkWhenSelectionLooseFocus) {
   outer->focus();
   UpdateAllLifecyclePhasesForTest();
   const SelectionInDOMTree& selection = Selection().GetSelectionInDOMTree();
-  EXPECT_EQ(selection.Base(),
-            Position(input, PositionAnchorType::kBeforeChildren));
+  EXPECT_EQ(selection.Base(), Position::FirstPositionInNode(*input));
   EXPECT_FALSE(ShouldShowCaret(caret));
 }
 

third_party/blink/renderer/core/editing/iterators/text_iterator_test.cc

@@ -337,14 +337,14 @@ TEST_P(TextIteratorTest, StartingAtNodeInShadowRoot) {
       GetDocument(), "host", shadow_content);
   Node* outer_div = GetDocument().getElementById("outer");
   Node* span_in_shadow = shadow_root->firstChild();
-  Position start(span_in_shadow, PositionAnchorType::kBeforeChildren);
+  Position start = Position::FirstPositionInNode(*span_in_shadow);
   Position end(outer_div, PositionAnchorType::kAfterChildren);
   EXPECT_EQ(
       "[ shadow][text][ iterator.]",
       IteratePartial<DOMTree>(start, end, EntersOpenShadowRootsBehavior()));
 
-  PositionInFlatTree start_in_flat_tree(span_in_shadow,
-                                        PositionAnchorType::kBeforeChildren);
+  PositionInFlatTree start_in_flat_tree =
+      PositionInFlatTree::FirstPositionInNode(*span_in_shadow);
   PositionInFlatTree end_in_flat_tree(outer_div,
                                       PositionAnchorType::kAfterChildren);
   EXPECT_EQ("[text][ shadow][ iterator.]",
@@ -362,14 +362,14 @@ TEST_P(TextIteratorTest, FinishingAtNodeInShadowRoot) {
       GetDocument(), "host", shadow_content);
   Node* outer_div = GetDocument().getElementById("outer");
   Node* span_in_shadow = shadow_root->firstChild();
-  Position start(outer_div, PositionAnchorType::kBeforeChildren);
+  Position start = Position::FirstPositionInNode(*outer_div);
   Position end(span_in_shadow, PositionAnchorType::kAfterChildren);
   EXPECT_EQ(
       "[Hello, ][ shadow]",
       IteratePartial<DOMTree>(start, end, EntersOpenShadowRootsBehavior()));
 
-  PositionInFlatTree start_in_flat_tree(outer_div,
-                                        PositionAnchorType::kBeforeChildren);
+  PositionInFlatTree start_in_flat_tree =
+      PositionInFlatTree::FirstPositionInNode(*outer_div);
   PositionInFlatTree end_in_flat_tree(span_in_shadow,
                                       PositionAnchorType::kAfterChildren);
   EXPECT_EQ("[Hello, ][text][ shadow]",

third_party/blink/renderer/core/editing/position.cc

@@ -660,7 +660,7 @@ Position ToPositionInDOMTree(const PositionInFlatTree& position) {
     case PositionAnchorType::kAfterAnchor:
       return Position::AfterNode(*anchor_node);
     case PositionAnchorType::kBeforeChildren:
-      return Position(anchor_node, PositionAnchorType::kBeforeChildren);
+      return Position::FirstPositionInNode(*anchor_node);
     case PositionAnchorType::kBeforeAnchor:
       return Position::BeforeNode(*anchor_node);
     case PositionAnchorType::kOffsetInAnchor: {
@@ -671,7 +671,7 @@ Position ToPositionInDOMTree(const PositionInFlatTree& position) {
       if (child)
         return Position(child->parentNode(), child->NodeIndex());
       if (!position.OffsetInContainerNode())
-        return Position(anchor_node, PositionAnchorType::kBeforeChildren);
+        return Position::FirstPositionInNode(*anchor_node);
 
       // |child| is null when the position is at the end of the children.
       // <div>foo|</div>

third_party/blink/renderer/core/editing/position_test.cc

@@ -198,9 +198,8 @@ TEST_F(PositionTest, ToPositionInFlatTreeWithShadowRoot) {
   EXPECT_EQ(PositionInFlatTree(host, PositionAnchorType::kAfterChildren),
             ToPositionInFlatTree(
                 Position(shadow_root, PositionAnchorType::kAfterChildren)));
-  EXPECT_EQ(PositionInFlatTree(host, PositionAnchorType::kBeforeChildren),
-            ToPositionInFlatTree(
-                Position(shadow_root, PositionAnchorType::kBeforeChildren)));
+  EXPECT_EQ(PositionInFlatTree::FirstPositionInNode(*host),
+            ToPositionInFlatTree(Position::FirstPositionInNode(*shadow_root)));
 }
 
 TEST_F(PositionTest,

third_party/blink/renderer/core/editing/serializers/styled_markup_serializer_test.cc

@@ -44,8 +44,8 @@ class StyledMarkupSerializerTest : public EditingTestBase {
 template <typename Strategy>
 std::string StyledMarkupSerializerTest::Serialize(
     const CreateMarkupOptions& options) {
-  PositionTemplate<Strategy> start = PositionTemplate<Strategy>(
-      GetDocument().body(), PositionAnchorType::kBeforeChildren);
+  PositionTemplate<Strategy> start =
+      PositionTemplate<Strategy>::FirstPositionInNode(*GetDocument().body());
   PositionTemplate<Strategy> end = PositionTemplate<Strategy>(
       GetDocument().body(), PositionAnchorType::kAfterChildren);
   return CreateMarkup(start, end, options).Utf8();

third_party/blink/renderer/core/layout/hit_test_result.cc

@@ -178,8 +178,8 @@ PositionWithAffinity HitTestResult::GetPosition() const {
     return PositionWithAffinity();
   if (inner_possibly_pseudo_node_->IsPseudoElement() &&
       inner_possibly_pseudo_node_->GetPseudoId() == kPseudoIdBefore) {
-    return PositionWithAffinity(MostForwardCaretPosition(
-        Position(inner_node_, PositionAnchorType::kBeforeChildren)));
+    return PositionWithAffinity(
+        MostForwardCaretPosition(Position::FirstPositionInNode(*inner_node_)));
   }
   if (box_fragment_ &&
       RuntimeEnabledFeatures::LayoutNGFullPositionForPointEnabled())