RenderTextHarfBuzz: Add support for multi line text selection.

ui/views/examples/label_example.h

 // Copyright (c) 2012 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 UI_VIEWS_EXAMPLES_LABEL_EXAMPLE_H_
 #define UI_VIEWS_EXAMPLES_LABEL_EXAMPLE_H_
 
 #include "base/macros.h"
 #include "ui/views/controls/button/button.h"
 #include "ui/views/controls/combobox/combobox_listener.h"
@@ skipping 40 matching lines @@
                          const char* name,
                          const char** strings,
                          int count);
 
   Textfield* textfield_;
   Combobox* alignment_;
   Combobox* elide_behavior_;
   std::vector<std::unique_ptr<ExampleComboboxModel>> example_combobox_models_;
   Checkbox* multiline_;
   Checkbox* shadows_;
+  Checkbox* selectable_;
   Label* custom_label_;
 
   DISALLOW_COPY_AND_ASSIGN(LabelExample);
 };
 
 }  // namespace examples
 }  // namespace views
 
 #endif  // UI_VIEWS_EXAMPLES_LABEL_EXAMPLE_H_