Fix line end caret w/o any following LayoutObject.

This patch fix ComputeInlineBoxPosition for the position that
points after line break and no LayoutObject after that by
fallback to previous position.
The fallback examples:
- "<br>|" to "|<br>"
- "<pre>foo\n|</pre>" to "<pre>foo|\n</pre>"

This change aligns legacy LocalCaretRect to NG.

Bug: 789870, 812535
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: Icb6cd9b8bc58b56a04d01eb22bdd58bd16ad5a01
Reviewed-on: https://chromium-review.googlesource.com/1215506
Commit-Queue: Yoichi Osato <yoichio@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590199}

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

@@ -283,12 +283,7 @@ bool NeedsLineEndAdjustment(
 // Returns the first InlineBoxPosition at next line of last InlineBoxPosition
 // in |layout_object| if it exists to avoid making InlineBoxPosition at end of
 // line.
-template <typename Strategy>
-InlineBoxPosition NextLinePositionOf(
-    const PositionWithAffinityTemplate<Strategy>& adjusted) {
-  const PositionTemplate<Strategy>& position = adjusted.GetPosition();
-  const LayoutText& layout_text =
-      ToLayoutTextOrDie(*position.AnchorNode()->GetLayoutObject());
+InlineBoxPosition NextLinePositionOf(const LayoutText& layout_text) {
   InlineTextBox* const last = layout_text.LastTextBox();
   if (!last)
     return InlineBoxPosition();
@@ -306,11 +301,26 @@ InlineBoxPosition NextLinePositionOf(
   return InlineBoxPosition();
 }
 
+template <typename Strategy>
+InlineBoxPosition ComputeInlineBoxPositionForLineEnd(
+    const PositionWithAffinityTemplate<Strategy>& adjusted) {
+  const LayoutText& layout_text = ToLayoutText(
+      *adjusted.GetPosition().AnchorNode()->GetLayoutObject());
+  const InlineBoxPosition next_line_position = NextLinePositionOf(layout_text);
+  if (next_line_position.inline_box)
+    return next_line_position;
+  // |adjusted| is after line end and no layout object after the position.
+  // Fall back to previous position.
+  DCHECK_GE(layout_text.TextLength(), 1u);
+  return ComputeInlineBoxPositionForTextNode(
+      &layout_text, layout_text.TextLength() - 1u, adjusted.Affinity());
+}
+
 template <typename Strategy>
 InlineBoxPosition ComputeInlineBoxPositionForInlineAdjustedPositionAlgorithm(
     const PositionWithAffinityTemplate<Strategy>& adjusted) {
   if (NeedsLineEndAdjustment(adjusted))
-    return NextLinePositionOf(adjusted);
+    return ComputeInlineBoxPositionForLineEnd(adjusted);
 
   const PositionTemplate<Strategy>& position = adjusted.GetPosition();
   DCHECK(!position.AnchorNode()->IsShadowRoot()) << adjusted;

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

@@ -698,11 +698,10 @@ TEST_P(ParameterizedLocalCaretRectTest, AfterLineBreak) {
       LocalCaretRect(second_br->GetLayoutObject(), LayoutRect(0, 10, 1, 10)),
       LocalCaretRectOfPosition(PositionWithAffinity(
           Position::AfterNode(*first_br), TextAffinity::kDownstream)));
-  EXPECT_EQ(LocalCaretRect(second_br->GetLayoutObject(),
-                           LayoutNGEnabled() ? LayoutRect(0, 10, 1, 10)
-                                             : LayoutRect(0, 0, 0, 0)),
-            LocalCaretRectOfPosition(PositionWithAffinity(
-                Position::AfterNode(*second_br), TextAffinity::kDownstream)));
+  EXPECT_EQ(
+      LocalCaretRect(second_br->GetLayoutObject(), LayoutRect(0, 10, 1, 10)),
+      LocalCaretRectOfPosition(PositionWithAffinity(
+          Position::AfterNode(*second_br), TextAffinity::kDownstream)));
 }
 
 TEST_P(ParameterizedLocalCaretRectTest, AfterLineBreakInPre) {
@@ -716,10 +715,7 @@ TEST_P(ParameterizedLocalCaretRectTest, AfterLineBreakInPre) {
   EXPECT_EQ(LocalCaretRect(foo->GetLayoutObject(), LayoutRect(0, 10, 1, 10)),
             LocalCaretRectOfPosition(PositionWithAffinity(
                 Position(foo, 4), TextAffinity::kDownstream)));
-  // TODO(yoichio): Legacy should return valid rect: crbug.com/812535.
-  EXPECT_EQ(LocalCaretRect(foo->GetLayoutObject(),
-                           LayoutNGEnabled() ? LayoutRect(0, 10, 1, 10)
-                                             : LayoutRect(0, 0, 0, 0)),
+  EXPECT_EQ(LocalCaretRect(foo->GetLayoutObject(), LayoutRect(0, 10, 1, 10)),
             LocalCaretRectOfPosition(PositionWithAffinity(
                 Position(foo, 5), TextAffinity::kDownstream)));
 }
@@ -738,9 +734,7 @@ TEST_P(ParameterizedLocalCaretRectTest, AfterLineBreakInPre2) {
   EXPECT_EQ(LocalCaretRect(br->GetLayoutObject(), LayoutRect(0, 10, 1, 10)),
             LocalCaretRectOfPosition(PositionWithAffinity(
                 Position(foo, 4), TextAffinity::kDownstream)));
-  EXPECT_EQ(LocalCaretRect(br->GetLayoutObject(), LayoutNGEnabled()
-                                                      ? LayoutRect(0, 10, 1, 10)
-                                                      : LayoutRect(0, 0, 0, 0)),
+  EXPECT_EQ(LocalCaretRect(br->GetLayoutObject(), LayoutRect(0, 10, 1, 10)),
             LocalCaretRectOfPosition(PositionWithAffinity(
                 Position::AfterNode(*br), TextAffinity::kDownstream)));
 }