Change NGInlineNodeEditor::SetTextWithOffset() to use character diff instead of offsets

This patch changes |NGInlineNodeEditor| to reuse |ShapeResult| before
and after changed region by equality of substring instead of calculating
it from offsets to handle generated line break markers, e.g. leading
spaces in pre-wrap, and increase chance to reuse, e.g. replacing
"abc" with "abX", before this patch we reuse nothing but after this
patch we reuse "ab".

This patch also gets rid of |NGInlineNodeData::can_use_flag_editing_|
because we don't use it.

Bug: 1131315
Change-Id: Ic4471340245522ced6b2a4d3d8bf43b23a2ff077
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2437831
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812062}

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

@@ -249,8 +249,11 @@ TEST_F(LayoutNGTextTest, SetTextWithOffsetDeleteWithGeneratedBreakOpportunity) {
   Text& text = To<Text>(*GetElementById("target")->firstChild());
   text.deleteData(2, 1, ASSERT_NO_EXCEPTION);  // remove "\n"
 
-  EXPECT_EQ("LayoutText has NeedsCollectInlines",
-            GetItemsAsString(*text.GetLayoutObject()));
+  EXPECT_EQ(
+      "*{'ab', ShapeResult=0+2}\n"
+      "{''}\n"
+      "{''}\n",
+      GetItemsAsString(*text.GetLayoutObject()));
 }
 
 // http://crbug.com/1123251

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

@@ -563,7 +563,6 @@ void NGInlineItemsBuilderTemplate<
           // after a forced break.
           if (item->Type() != NGInlineItem::kControl ||
               text_[item->StartOffset()] != kNewlineCharacter) {
-            can_use_fast_editing_ = false;
             AppendGeneratedBreakOpportunity(layout_object);
           }
         }
@@ -1236,7 +1235,6 @@ void NGInlineItemsBuilderTemplate<
   // |SegmentText()| will analyze the text and reset |is_bidi_enabled_| if it
   // doesn't contain any RTL characters.
   data->is_bidi_enabled_ = MayBeBidiEnabled();
-  data->can_use_fast_editing_ = CanUseFastEditing();
   // Note: Even if |IsEmptyInline()| is true, |text_| isn't empty, e.g. it
   // holds U+FFFC(ORC) for float or abspos.
   data->has_line_even_if_empty_ =

third_party/blink/renderer/core/layout/ng/inline/ng_inline_items_builder.h

@@ -56,9 +56,6 @@ class NGInlineItemsBuilderTemplate {
   // Returns whether the items contain any Bidi controls.
   bool HasBidiControls() const { return has_bidi_controls_; }
 
-  // Returns whether the items contain any generated break opportunity.
-  bool CanUseFastEditing() const { return can_use_fast_editing_; }
-
   // Returns if the inline node has no content. For example:
   // <span></span> or <span><float></float></span>.
   bool IsEmptyInline() const { return is_empty_inline_; }
@@ -185,7 +182,6 @@ class NGInlineItemsBuilderTemplate {
 
   bool has_bidi_controls_ = false;
   bool has_ruby_ = false;
-  bool can_use_fast_editing_ = true;
   bool is_empty_inline_ = true;
   bool is_block_level_ = true;
   bool changes_may_affect_earlier_lines_ = false;

third_party/blink/renderer/core/layout/ng/inline/ng_inline_node_data.h

@@ -22,7 +22,6 @@ struct CORE_EXPORT NGInlineNodeData : NGInlineItemsData {
     return static_cast<TextDirection>(base_direction_);
   }
 
-  bool CanUseFastEditing() const { return can_use_fast_editing_; }
   bool HasLineEvenIfEmpty() const { return has_line_even_if_empty_; }
   bool HasRuby() const { return has_ruby_; }
   bool IsEmptyInline() const { return is_empty_inline_; }
@@ -59,9 +58,6 @@ struct CORE_EXPORT NGInlineNodeData : NGInlineItemsData {
   unsigned is_bidi_enabled_ : 1;
   unsigned base_direction_ : 1;  // TextDirection
 
-  // True if we can use fast editing path.
-  unsigned can_use_fast_editing_ : 1;
-
   // True if there are no inline item items and the associated block is root
   // editable element or having "-internal-empty-line-height:fabricated",
   // e.g. <div contenteditable></div>, <input type=button value="">

third_party/blink/web_tests/editing/inserting/typing_break_opportunity-expected.html

+<!doctype html>
+<script src="../../resources/ahem.js"></script>
+<style>
+.sample {
+    border: solid 1px; green;
+    font: 20px monospace;
+    padding: 5px;
+    white-space: pre-wrap;
+}
+</style>
+<div class="sample" id="target">XYZ bc</div>
+<br>
+<div class="sample">XYZ bc</div>

third_party/blink/web_tests/editing/inserting/typing_break_opportunity.html

+<!doctype html>
+<script src="../../resources/ahem.js"></script>
+<style>
+.sample {
+    border: solid 1px; green;
+    font: 20px monospace;
+    padding: 5px;
+    white-space: pre-wrap;
+}
+</style>
+<div class="sample" id="target"> bc</div>
+<br>
+<div class="sample">XYZ bc</div>
+<script>
+const target = document.getElementById('target');
+const text = target.firstChild;
+document.body.offsetHeight;
+text.insertData(0, 'XYZ');
+</script>