[LayoutNG] Make all CharacterIteratorTest pass with LayoutNG

CharacterIteratorTest.GetPositionWithEmitChar16Before used to fail with
LayoutNG enabled, because it's actually a buggy case in legacy layout
where TextIterator emits an extra character.

This patch makes the test case skip the extra character when LayoutNG
is enabled, and hence allows it to pass.

Bug: 810579
Change-Id: Ie111735af3c94fe7b47eed7a993d1d374612caa6
Reviewed-on: https://chromium-review.googlesource.com/c/1340862Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609478}

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

@@ -283,8 +283,7 @@ TEST_P(ParameterizedCharacterIteratorTest,
   EXPECT_TRUE(it.AtEnd());
 }
 
-// TODO(xiaochengh): Fix it in LayoutNG
-TEST_F(CharacterIteratorTest, GetPositionWithEmitChar16Before) {
+TEST_P(ParameterizedCharacterIteratorTest, GetPositionWithEmitChar16Before) {
   InsertStyleElement("b { white-space: pre; }");
   SetBodyContent("a   <b> c</b>");
 
@@ -307,15 +306,17 @@ TEST_F(CharacterIteratorTest, GetPositionWithEmitChar16Before) {
   EXPECT_EQ(Position(text_a, 1), it.StartPosition());
   EXPECT_EQ(Position(text_a, 2), it.EndPosition());
 
-  // TODO(editing-dev): We should know why we emit a space character for
-  // "white-space: pre" element after trailing whitespace.
-  // A space character emitted by |EmitChar16Before()|.
+  if (!LayoutNGEnabled()) {
+    // TODO(editing-dev): TextIterator with legacy layout incorrectly emits a
+    // space character for "white-space: pre" element after trailing whitespace.
+    // A space character emitted by |EmitChar16Before()|. Fix it.
     ASSERT_FALSE(it.AtEnd());
     it.Advance(1);
     EXPECT_EQ(Position(text_c, 0), it.GetPositionBefore());
     EXPECT_EQ(Position(text_c, 0), it.GetPositionAfter());
     EXPECT_EQ(Position(text_c, 0), it.StartPosition());
     EXPECT_EQ(Position(text_c, 0), it.EndPosition());
+  }
 
   ASSERT_FALSE(it.AtEnd());
   it.Advance(1);