[LayoutNG] Implement EmitsSpaceForNbsp behavior for TextIterator

Our NG TextIterator didn't implement the EmitsSpaceForNbsp behavior.
This patch implements it.

Change-Id: I76e7531ee013494566c15417658042b012462690
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1506972
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638594}

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

@@ -75,6 +75,10 @@ TextIteratorBehavior EmitsCharactersBetweenAllVisiblePositionsBehavior() {
       .Build();
 }
 
+TextIteratorBehavior EmitsSpaceForNbspBehavior() {
+  return TextIteratorBehavior::Builder().SetEmitsSpaceForNbsp(true).Build();
+}
+
 struct DOMTree : NodeTraversal {
   using PositionType = Position;
   using TextIteratorType = TextIterator;
@@ -1151,5 +1155,10 @@ TEST_P(TextIteratorTest, TextOffsetMappingAndFlatTree) {
       Iterate<FlatTree>(EmitsCharactersBetweenAllVisiblePositionsBehavior()));
 }
 
+TEST_P(TextIteratorTest, EmitsSpaceForNbsp) {
+  SetBodyContent("foo &nbsp;bar");
+  EXPECT_EQ("[foo  bar]", Iterate<DOMTree>(EmitsSpaceForNbspBehavior()));
+}
+
 }  // namespace text_iterator_test
 }  // namespace blink

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

@@ -60,8 +60,8 @@ StringAndOffsetRange ComputeTextAndOffsetsForEmission(
     String string = mapping.GetText().Substring(
         unit.TextContentStart(),
         unit.TextContentEnd() - unit.TextContentStart());
-    // TODO(xiaochengh): This seems wrong... Add real handling.
-    return {string, 0, 0};
+    string.Replace(kNoBreakSpaceCharacter, kSpaceCharacter);
+    return {string, 0, string.length()};
   }
   return {mapping.GetText(), unit.TextContentStart(), unit.TextContentEnd()};
 }