Implement clipboard features in views textfield.

views/controls/textfield/textfield_views_model.h

Index: views/controls/textfield/textfield_views_model.h
diff --git a/views/controls/textfield/textfield_views_model.h b/views/controls/textfield/textfield_views_model.h
index 219a8c721617014cf9360b03163f873e11c9377f..c1fa375c216b4261877d759d63a92b4c6c47178e 100644
--- a/views/controls/textfield/textfield_views_model.h
+++ b/views/controls/textfield/textfield_views_model.h
@@ -126,6 +126,17 @@ class TextfieldViewsModel {
     return GetVisibleText(0U, text_.length());
   }
 
+  // Cuts the currently selected text and puts it to clipboard. Returns true
+  // if text has changed after cutting.
+  bool Cut();
+
+  // Copies the currently selected text and puts it to clipboard.
+  void Copy();
+
+  // Pastes text from the clipboard at current cursor position. Returns true
+  // if text has changed after pasting.
+  bool Paste();
+
  private:
   friend class NativeTextfieldViews;