Make NGInlineItemsBuilderTempalte not to use BoxInfo for offset mapping

Because of offset mapping doesn't use |BoxInfo| and creating |BoxInfo| also
causes side-effect to mark layout objects |InNGInlineFormattingContext| this
patch changes |NGInlineItemsBuilderTempalte<T>| not to use |BoxInfo| for
offset mapping.

This patch is follow-up the patch[1] and preparation of the patch[2].

[1] http://crrev.com/c/1327582 Make NGOffsetMapping available for non-LayoutNG
LayoutBlockFlow
[2] http://crrev.com/c/1337224 Utilize NGInlineNode::GetOffsetMapping() in
Element#innerText

Change-Id: Id5a9d9c4e998261cfa57ec24fc9e268b002a8617
Reviewed-on: https://chromium-review.googlesource.com/c/1341293
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609193}

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

@@ -4,6 +4,8 @@
 
 #include "third_party/blink/renderer/core/layout/ng/inline/ng_inline_items_builder.h"
 
+#include <type_traits>
+
 #include "third_party/blink/renderer/core/layout/layout_object.h"
 #include "third_party/blink/renderer/core/layout/layout_text.h"
 #include "third_party/blink/renderer/core/layout/ng/inline/layout_ng_text.h"
@@ -13,6 +15,12 @@
 
 namespace blink {
 
+// Returns true if items builder is used for other than offset mapping.
+template <typename OffsetMappingBuilder>
+bool NGInlineItemsBuilderTemplate<OffsetMappingBuilder>::NeedsBoxInfo() {
+  return !std::is_same<NGOffsetMappingBuilder, OffsetMappingBuilder>::value;
+}
+
 template <typename OffsetMappingBuilder>
 NGInlineItemsBuilderTemplate<
     OffsetMappingBuilder>::~NGInlineItemsBuilderTemplate() {
@@ -936,6 +944,9 @@ void NGInlineItemsBuilderTemplate<OffsetMappingBuilder>::EnterInline(
 
   AppendOpaque(NGInlineItem::kOpenTag, style, node);
 
+  if (!NeedsBoxInfo())
+    return;
+
   // Set |ShouldCreateBoxFragment| of the parent box if needed.
   BoxInfo* current_box =
       &boxes_.emplace_back(items_->size() - 1, items_->back());
@@ -965,7 +976,8 @@ void NGInlineItemsBuilderTemplate<OffsetMappingBuilder>::ExitInline(
 
   AppendOpaque(NGInlineItem::kCloseTag, node->Style(), node);
 
-  boxes_.pop_back();
+  if (NeedsBoxInfo())
+    boxes_.pop_back();
 
   Exit(node);
 

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

@@ -111,6 +111,8 @@ class NGInlineItemsBuilderTemplate {
   void SetIsSymbolMarker(bool b);
 
  private:
+  static bool NeedsBoxInfo();
+
   Vector<NGInlineItem>* items_;
   StringBuilder text_;