[LayoutNG] Move NGCaretNavigator::GetItem() to NGInlineItemsData

The function is a general function for probing NGInlineItemsData. Hence,
this patch moves it to NGInlineItemsData, where it better resides.

This patch follows from kojii's comments in crrev.com/c/1436486

Bug: 894651
Change-Id: Icdc625c0dbddb219d484e987f4ea02076045a4c8
Reviewed-on: https://chromium-review.googlesource.com/c/1440501
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Auto-Submit: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626790}

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

@@ -33,26 +33,11 @@ bool NGCaretNavigator::IsBidiEnabled() const {
   return GetData().IsBidiEnabled();
 }
 
-const NGInlineItem& NGCaretNavigator::GetItem(unsigned index) const {
-  const auto& items = GetData().items;
-  const NGInlineItem* item =
-      std::lower_bound(items.begin(), items.end(), index,
-                       [](const NGInlineItem& item, unsigned index) {
-                         if (item.StartOffset() > index)
-                           return false;
-                         return item.EndOffset() <= index;
-                       });
-  DCHECK_NE(item, items.end());
-  DCHECK_LE(item->StartOffset(), index);
-  DCHECK_LT(index, item->EndOffset());
-  return *item;
-}
-
 UBiDiLevel NGCaretNavigator::BidiLevelAt(unsigned index) const {
   DCHECK_LT(index, GetText().length());
   if (!IsBidiEnabled())
     return 0;
-  return GetItem(index).BidiLevel();
+  return GetData().FindItemForTextOffset(index).BidiLevel();
 }
 
 TextDirection NGCaretNavigator::TextDirectionAt(unsigned index) const {

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

@@ -275,4 +275,20 @@ void NGInlineItem::SetEndCollapseType(NGCollapseType type, bool is_newline) {
   is_end_collapsible_newline_ = is_newline;
 }
 
+const NGInlineItem& NGInlineItemsData::FindItemForTextOffset(
+    unsigned offset) const {
+  DCHECK_LT(offset, text_content.length());
+  const NGInlineItem* item =
+      std::lower_bound(items.begin(), items.end(), offset,
+                       [](const NGInlineItem& item, unsigned offset) {
+                         if (item.StartOffset() > offset)
+                           return false;
+                         return item.EndOffset() <= offset;
+                       });
+  DCHECK_NE(item, items.end());
+  DCHECK_LE(item->StartOffset(), offset);
+  DCHECK_LT(offset, item->EndOffset());
+  return *item;
+}
+
 }  // namespace blink

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

@@ -224,6 +224,11 @@ struct CORE_EXPORT NGInlineItemsData {
   void AssertEndOffset(unsigned index, unsigned offset) const {
     items[index].AssertEndOffset(offset);
   }
+
+  // Returns the non-zero-length inline item whose |StartOffset() <= offset| and
+  // |EndOffset() > offset|, namely, contains the character at |offset|.
+  // Note: This function is not a trivial getter, but does a binary search.
+  const NGInlineItem& FindItemForTextOffset(unsigned offset) const;
 };
 
 }  // namespace blink