Templatize NGInlineItemsBuilder to take a OffsetMappingBuilder parameter

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

Index: third_party/WebKit/Source/core/layout/ng/inline/empty_offset_mapping_builder.h
diff --git a/third_party/WebKit/Source/core/layout/ng/inline/empty_offset_mapping_builder.h b/third_party/WebKit/Source/core/layout/ng/inline/empty_offset_mapping_builder.h
new file mode 100644
index 0000000000000000000000000000000000000000..825ede41c6f6105293891729bfe01dfb7f3a55c4
--- /dev/null
+++ b/third_party/WebKit/Source/core/layout/ng/inline/empty_offset_mapping_builder.h
@@ -0,0 +1,28 @@
+// 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;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(EmptyOffsetMappingBuilder);
+};
+
+}  // namespace blink
+
+#endif  // EmptyOffsetMappingBuilder_h