views::Textfield: Implement yank editing command.

ui/views/test/views_test_helper.cc

Index: ui/views/test/views_test_helper.cc
diff --git a/ui/views/test/views_test_helper.cc b/ui/views/test/views_test_helper.cc
index 75588a6cb7f0d338bc55788cc8a4b7d1e71be643..7490b569f8a615c62b0e21d49735d081080db8ef 100644
--- a/ui/views/test/views_test_helper.cc
+++ b/ui/views/test/views_test_helper.cc
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "ui/views/controls/textfield/textfield_model.h"
 #include "ui/views/test/views_test_helper.h"
 
 namespace views {
@@ -10,6 +11,9 @@ ViewsTestHelper::ViewsTestHelper() {
 }
 
 ViewsTestHelper::~ViewsTestHelper() {
+  // Clear kill buffer used for "Yank" text editing command so that no state
+  // persists between tests.
+  TextfieldModel::ClearKillBufferForTesting();

[msw, 2016/07/22 17:44:03]

Would it be sufficient to clear this in Textfield[Model]Test::TearDown, or at
the start/end of the yank text fixtures? Other unit test fixtures that actually
use yank could do the same, and any other unit test fixtures that don't actually
use yank shouldn't be affected, right?

[karandeepb, 2016/07/25 06:38:11]

Done. 

 }
 
 void ViewsTestHelper::SetUp() {