Avoid having LayoutText for Text::splitText()

This patch changes |Text:splitText()| to avoid having empty |LayoutText|
as other text modifying functions, e.g. deleteData(), replaceData() to
reduce changes that AX tree having AX objects with empty |LayoutText|.

Note: The root cause of issue 1149171 is |Range#insertNodes()| calling
|Text#splitText()| with offset 0.

Bug: 1149171
Change-Id: Ibfecb14111ff16f3901fe23cdba6d3fcae1ddda1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2623371
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842890}

third_party/blink/renderer/core/dom/text.cc

@@ -124,8 +124,13 @@ Text* Text::splitText(unsigned offset, ExceptionState& exception_state) {
   if (exception_state.HadException())
     return nullptr;
 
-  if (GetLayoutObject())
+  if (GetLayoutObject()) {
     GetLayoutObject()->SetTextWithOffset(DataImpl(), 0, old_str.length());
+    if (data().IsEmpty()) {
+      // To avoid |LayoutText| has empty text, we rebuild layout tree.
+      SetForceReattachLayoutTree();
+    }
+  }
 
   if (parentNode())
     GetDocument().DidSplitTextNode(*this);

third_party/blink/renderer/core/dom/text_test.cc

@@ -4,6 +4,7 @@
 
 #include "third_party/blink/renderer/core/dom/text.h"
 
+#include "third_party/blink/renderer/bindings/core/v8/v8_binding_for_testing.h"
 #include "third_party/blink/renderer/core/dom/range.h"
 #include "third_party/blink/renderer/core/editing/testing/editing_test_base.h"
 #include "third_party/blink/renderer/core/html/html_pre_element.h"
@@ -40,6 +41,22 @@ TEST_F(TextTest, RemoveFirstLetterPseudoElementWhenNoLetter) {
   EXPECT_FALSE(text->GetLayoutObject()->IsTextFragment());
 }
 
+TEST_F(TextTest, splitTextToEmpty) {
+  V8TestingScope scope;
+
+  SetBodyContent("<p id=sample>ab</p>");
+  const Element& sample = *GetElementById("sample");
+  Text& text = *To<Text>(sample.firstChild());
+  // |new_text| is after |text|.
+  Text& new_text = *text.splitText(0, ASSERT_NO_EXCEPTION);
+
+  UpdateAllLifecyclePhasesForTest();
+  EXPECT_EQ("", text.data());
+  EXPECT_FALSE(text.GetLayoutObject());
+  EXPECT_EQ("ab", new_text.data());
+  EXPECT_TRUE(new_text.GetLayoutObject());
+}
+
 TEST_F(TextTest, TextLayoutObjectIsNeeded_CannotHaveChildren) {
   SetBodyContent("<img id=image>");
   UpdateAllLifecyclePhasesForTest();

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

@@ -424,8 +424,8 @@ TEST_P(ParameterizedLayoutTextFragmentTest, SetTextWithFirstLetter) {
                   ->IsRemainingTextLayoutObject());
   ASSERT_TRUE(letter_a.GetLayoutObject()->GetFirstLetterPart());
   EXPECT_EQ("a", letter_a.GetLayoutObject()->GetFirstLetterPart()->GetText());
-  EXPECT_TRUE(letter_x.GetLayoutObject()->IsTextFragment());
-  EXPECT_FALSE(letter_x.GetLayoutObject()->GetFirstLetterPart());
+  EXPECT_FALSE(letter_x.GetLayoutObject())
+      << "We don't have layout text for empty Text node.";
 
   // Make <div>"x" "a"</div>
   letter_x.setTextContent("x");