EXPERIMENT TextIterator built on Layout NG offset mapping

third_party/WebKit/Source/core/layout/ng/inline/ng_offset_mapping_result.h

Index: third_party/WebKit/Source/core/layout/ng/inline/ng_offset_mapping_result.h
diff --git a/third_party/WebKit/Source/core/layout/ng/inline/ng_offset_mapping_result.h b/third_party/WebKit/Source/core/layout/ng/inline/ng_offset_mapping_result.h
index 12b0becb896cb0e938da6964c3ee1964c694aa1a..a4a3e541bd79c2409890dbdeb6906c38c12d7a09 100644
--- a/third_party/WebKit/Source/core/layout/ng/inline/ng_offset_mapping_result.h
+++ b/third_party/WebKit/Source/core/layout/ng/inline/ng_offset_mapping_result.h
@@ -47,6 +47,20 @@ struct NGOffsetMappingUnit {
   unsigned dom_end = 0;
   unsigned text_content_start = 0;
   unsigned text_content_end = 0;
+
+  unsigned DOMToTextContentOffset(unsigned dom_offset) const {
+    switch (type) {
+      case NGOffsetMappingUnitType::kIdentity:
+        return dom_offset - dom_start + text_content_start;
+      case NGOffsetMappingUnitType::kCollapsed:
+        return text_content_start;
+      case NGOffsetMappingUnitType::kExpanded:
+        return dom_offset == dom_start ? text_content_start : text_content_end;
+    }
+    // Add |return| in this unreachable patch to make Windows compiler happy.
+    NOTREACHED();
+    return 0;
+  }
 };
 
 // An NGOffsetMappingResult stores the units of a LayoutNGBlockFlow in sorted
@@ -56,6 +70,10 @@ struct NGOffsetMappingUnit {
 struct NGOffsetMappingResult {
   DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
 
+  // Returns the mapping unit whose owner is the node and dom offset range
+  // contains the given offset. Returns the last one if multiple units qualify.
+  const NGOffsetMappingUnit* GetMappingUnitForDOMOffset(const Node&, unsigned);
+
   Vector<NGOffsetMappingUnit> units;
   HashMap<const LayoutText*, std::pair<unsigned, unsigned>> ranges;
 };