Make NGInlineItemsBuilder construct whitespace-collapsed offset mapping

third_party/WebKit/Source/core/layout/ng/api/ng_offset_mapping_builder.h

Index: third_party/WebKit/Source/core/layout/ng/api/ng_offset_mapping_builder.h
diff --git a/third_party/WebKit/Source/core/layout/ng/api/ng_offset_mapping_builder.h b/third_party/WebKit/Source/core/layout/ng/api/ng_offset_mapping_builder.h
new file mode 100644
index 0000000000000000000000000000000000000000..0efde3353d1a62de64363ef549cd78149c715539
--- /dev/null
+++ b/third_party/WebKit/Source/core/layout/ng/api/ng_offset_mapping_builder.h
@@ -0,0 +1,30 @@
+// 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 NGOffsetMappingBuilder_h
+#define NGOffsetMappingBuilder_h
+
+#include "core/CoreExport.h"
+#include "platform/wtf/Allocator.h"
+
+namespace blink {
+
+// TODO(xiaochengh): Documentation.
+class CORE_EXPORT NGOffsetMappingBuilder {
+  STACK_ALLOCATED();
+
+ public:
+  NGOffsetMappingBuilder();
+  virtual ~NGOffsetMappingBuilder();

[yosin_UTC9, 2017/06/22 03:31:04]

Why interface? Do you want to introduce DoNothingOffsetMappingBuilder to avoid
|if (mapping_builder_) ...|?
It seems we still have |if (mapping_builder_) ...| in |NGInlineItemBuilder|.
Maybe for testing?

If using an interface is just for testing, it is better to have concrete class
and having member test only(?) function to access
result mapping.

[Xiaocheng, 2017/06/22 03:36:10]

I would like to have different types of offset mapping builder. Some builders in
my mind are:

1. For offset mapping before and white space collapsing
2. For offset mapping before and after text-transform
3. For offset mapping from DOM to after white space collapsing, which is
obtained by compositing the above two

So I intentionally leave some flexibility in the class so that it may grow into
something powerful.

[yosin_UTC9, 2017/06/22 03:44:22]

Editing is case 3. What cases do use 1 and 2?

+
+  virtual void AppendBijection(unsigned length);
+  virtual void AppendCollapsed(unsigned length);
+  virtual void CollapseLastCharacter();
+
+  DISALLOW_COPY_AND_ASSIGN(NGOffsetMappingBuilder);

[yosin_UTC9, 2017/06/22 03:31:04]

nit: |DISALLOW_...| should be in private section.

[Xiaocheng, 2017/06/22 03:36:10]

Will do.

+};
+
+}  // namespace blink
+
+#endif  // OffsetMappingBuilder_h