Revise condition of using fast path in LayoutText::SetTextWithOffset()

This patch makes |LayoutText::SetTextWithOffset()| to use fast path in
case of using generated break opportunities for spaces after newline
in same layout text.

There are three cases we use generated break opportunities:
 1. In white-space:pre-wrap: leading spaces after newline
 2. In white-space:pre-wrap: spaces after newline
 3. collapsible space after newline in white-space:pre-wrap
    <b><i><s>ab\n</s></i>\n</b>

The CL[1] makes |LayoutText::SetTextWithOffset()| to use slow path
because of it is hard to handle case 3 even if we can handle case 1 and
2. In this CL, we use fast path for case 1 and 2 but case 3.

[1] http://crrev.com/c/2395136: Make LayoutText::SetTextWithOffset() to
use slow path for generated break opportunities

Bug: 1125640, 1125641
Change-Id: I22ee9c1aa6b7ff5f57c08524ee7ac704ecb5db6a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2397036Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804840}

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

@@ -277,7 +277,6 @@ void NGInlineItemsBuilderTemplate<OffsetMappingBuilder>::
   typename OffsetMappingBuilder::SourceNodeScope scope(&mapping_builder_,
                                                        nullptr);
   NGInlineItem& item = AppendBreakOpportunity(layout_object);
-  has_generated_break_opportunity_ = true;
   item.SetIsGeneratedForLineBreak();
   item.SetEndCollapseType(NGInlineItem::kOpaqueToCollapsing);
 }
@@ -568,6 +567,7 @@ void NGInlineItemsBuilderTemplate<
           // after a forced break.
           if (item->Type() != NGInlineItem::kControl ||
               text_[item->StartOffset()] != kNewlineCharacter) {
+            can_use_fast_editing_ = false;
             AppendGeneratedBreakOpportunity(layout_object);
           }
         }
@@ -1240,7 +1240,7 @@ 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->has_generated_break_opportunity_ = HasGeneratedBreakOpportunity();
+  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

@@ -57,9 +57,7 @@ class NGInlineItemsBuilderTemplate {
   bool HasBidiControls() const { return has_bidi_controls_; }
 
   // Returns whether the items contain any generated break opportunity.
-  bool HasGeneratedBreakOpportunity() const {
-    return has_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>.
@@ -187,7 +185,7 @@ class NGInlineItemsBuilderTemplate {
 
   bool has_bidi_controls_ = false;
   bool has_ruby_ = false;
-  bool has_generated_break_opportunity_ = 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.cc

@@ -523,7 +523,7 @@ class NGInlineNodeDataEditor final {
         block_flow_->GetDocument().NeedsLayoutTreeUpdate() ||
         !block_flow_->GetNGInlineNodeData() ||
         block_flow_->GetNGInlineNodeData()->text_content.IsNull() ||
-        block_flow_->GetNGInlineNodeData()->HasGeneratedBreakOpportunity())
+        !block_flow_->GetNGInlineNodeData()->CanUseFastEditing())
       return nullptr;
 
     // Because of current text content has secured text, e.g. whole text is

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

@@ -22,10 +22,7 @@ struct CORE_EXPORT NGInlineNodeData : NGInlineItemsData {
     return static_cast<TextDirection>(base_direction_);
   }
 
-  bool HasGeneratedBreakOpportunity() const {
-    return has_generated_break_opportunity_;
-  }
-
+  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_; }
@@ -62,9 +59,8 @@ struct CORE_EXPORT NGInlineNodeData : NGInlineItemsData {
   unsigned is_bidi_enabled_ : 1;
   unsigned base_direction_ : 1;  // TextDirection
 
-  // True if text content has U+200B, zero width space, representing generated
-  // break opportunity.
-  unsigned has_generated_break_opportunity_ : 1;
+  // 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",