[LayoutNG] Make NGInlineCursor::PositionForPointInChild() to work with...

[LayoutNG] Make NGInlineCursor::PositionForPointInChild() to work with inline-block that has block children

This patch changes |NGPaintFragment::PositionForPoint()| to work with block
children inline-block to make |NGInlineCursor::PositionForPointInChild()| to
work with it.

Bug: 1096110
Change-Id: Ia7d070fe5287a20868cafd4eac370e83a4d81fa3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2286092
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786605}

third_party/blink/renderer/core/layout/ng/inline/ng_inline_cursor.cc

@@ -934,12 +934,11 @@ PositionWithAffinity NGInlineCursor::PositionForPointInChild(
     case NGFragmentItem::kBox:
       if (const NGPhysicalBoxFragment* box_fragment =
               child_item.BoxFragment()) {
-        // We must fallback to legacy for old layout roots. We also fallback (to
-        // LayoutNGMixin::PositionForPoint()) for NG block layout, so that we
-        // can utilize LayoutBlock::PositionForPoint() that resolves the
-        // position in block layout.
-        // TODO(xiaochengh): Don't fallback to legacy for NG block layout.
         if (!box_fragment->IsInlineBox()) {
+          // In case of inline block with with block formatting context that
+          // has block children[1].
+          // Example: <b style="display:inline-block"><div>b</div></b>
+          // [1] NGInlineCursorTest.PositionForPointInChildBlockChildren
           return child_item.GetLayoutObject()->PositionForPoint(
               point_in_container - child_item.OffsetInContainerBlock());
         }

third_party/blink/renderer/core/layout/ng/inline/ng_inline_cursor_test.cc

@@ -884,6 +884,18 @@ TEST_P(NGInlineCursorTest, PositionForPointInChildVerticalRTL) {
             cursor.PositionForPointInChild(left_top + PhysicalOffset(0, 25)));
 }
 
+// For http://crbug.com/1096110
+TEST_P(NGInlineCursorTest, PositionForPointInChildBlockChildren) {
+  InsertStyleElement("b { display: inline-block; }");
+  // Note: <b>.ChildrenInline() == false
+  NGInlineCursor cursor =
+      SetupCursor("<div id=root>a<b id=target><div>x</div></b></div>");
+  const Element& target = *GetElementById("target");
+  cursor.MoveTo(*target.GetLayoutObject());
+  EXPECT_EQ(PositionWithAffinity(Position(target, 0)),
+            cursor.PositionForPointInChild(PhysicalOffset()));
+}
+
 TEST_P(NGInlineCursorTest, Previous) {
   // TDOO(yosin): Remove <style> once NGFragmentItem don't do culled inline.
   InsertStyleElement("b { background: gray; }");

third_party/blink/renderer/core/paint/ng/ng_paint_fragment.cc

@@ -996,10 +996,14 @@ PositionWithAffinity NGPaintFragment::PositionForPoint(
     return PositionForPointInText(point);
 
   if (PhysicalFragment().IsBlockFlow()) {
-    // We current fall back to legacy for block formatting contexts, so we
-    // should reach here only for inline formatting contexts.
-    // TODO(xiaochengh): Do not fall back.
-    return PositionForPointInInlineFormattingContext(point);
+    const LayoutObject& layout_object = *PhysicalFragment().GetLayoutObject();
+    if (layout_object.ChildrenInline())
+      return PositionForPointInInlineFormattingContext(point);
+    // |NGInlineCursor::PositionForPointInChild()| calls this function with
+    // inline block with with block formatting context that has block
+    // children[1], e.g: <b style="display:inline-block"><div>b</div></b>
+    // [1] NGInlineCursorTest.PositionForPointInChildBlockChildren
+    return layout_object.PositionForPoint(point);
   }
 
   DCHECK(PhysicalFragment().IsInline() || PhysicalFragment().IsLineBox());