Make NGInlineItemsBuilder construct whitespace-collapsed offset mapping

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

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef EmptyOffsetMappingBuilder_h
 #define EmptyOffsetMappingBuilder_h
 
 #include "platform/wtf/Allocator.h"
 
 namespace blink {
 
 // A mock class providing all APIs of an offset mapping builder, but not doing
 // anything. For templates functions/classes that can optionally create an
 // offset mapping, this mock class is passed to create an instantiation that
 // does not create any offset mapping.
 class EmptyOffsetMappingBuilder {
   STACK_ALLOCATED();
 
  public:
   EmptyOffsetMappingBuilder() = default;
+  void AppendIdentityMapping(unsigned) {}
+  void AppendCollapsedMapping(unsigned) {}
+  void CollapseTrailingSpace(unsigned) {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(EmptyOffsetMappingBuilder);
 };
 
 }  // namespace blink
 
 #endif  // EmptyOffsetMappingBuilder_h