views::Textfield: Implement yank editing command.

ui/views/controls/textfield/textfield_model.h

Index: ui/views/controls/textfield/textfield_model.h
diff --git a/ui/views/controls/textfield/textfield_model.h b/ui/views/controls/textfield/textfield_model.h
index df3e9754e2d52c1e51949b542cf3d2552c56dfc4..d01aba2fb39796348bcaf677f6fc8ee7c2deccad 100644
--- a/ui/views/controls/textfield/textfield_model.h
+++ b/ui/views/controls/textfield/textfield_model.h
@@ -95,15 +95,17 @@ class VIEWS_EXPORT TextfieldModel {
 
   // Deletes the first character after the current cursor position (as if, the
   // the user has pressed delete key in the textfield). Returns true if
-  // the deletion is successful.
+  // the deletion is successful. If |add_to_kill_buffer| is true, the deleted
+  // text is copied to the kill buffer.
   // If there is composition text, it'll be deleted instead.
-  bool Delete();
+  bool Delete(bool add_to_kill_buffer = false);
 
   // Deletes the first character before the current cursor position (as if, the
   // the user has pressed backspace key in the textfield). Returns true if
-  // the removal is successful.
+  // the removal is successful. If |add_to_kill_buffer| is true, the deleted
+  // text is copied to the kill buffer.
   // If there is composition text, it'll be deleted instead.
-  bool Backspace();
+  bool Backspace(bool add_to_kill_buffer = false);
 
   // Cursor related methods.
 
@@ -182,6 +184,10 @@ class VIEWS_EXPORT TextfieldModel {
   // changed.
   bool Transpose();
 
+  // Pastes text from the kill buffer at the current cursor position or
+  // selection.
+  bool Yank();
+
   // Tells if any text is selected, even if the selection is in composition
   // text.
   bool HasSelection() const;