views::Textfield: Implement yank editing command.

ui/views/cocoa/bridged_content_view.mm

Index: ui/views/cocoa/bridged_content_view.mm
diff --git a/ui/views/cocoa/bridged_content_view.mm b/ui/views/cocoa/bridged_content_view.mm
index 8aab6665eeab5ce360fa1776c19013a22fd11d31..920980bef4ff2fd2caccca6b3b58806752b5ec9f 100644
--- a/ui/views/cocoa/bridged_content_view.mm
+++ b/ui/views/cocoa/bridged_content_view.mm
@@ -1029,6 +1029,13 @@ ui::KeyEvent GetCharacterEventFromNSEvent(NSEvent* event) {
   [self deleteToEndOfLine:sender];
 }
 
+- (void)yank:(id)sender {
+  [self handleAction:ui::TextEditCommand::YANK
+             keyCode:ui::VKEY_Y

[karandeepb, 2016/07/01 05:49:16]

Again is it ok to give this key code for Ctrl+Y? Before executing the scheduled
command, Textfield::OnKeyPressed passes the key event to
TextfieldController::HandleKeyEvent. Since Ctrl+Y can be interpreted in
different ways, I may be safer to give this a dummy key code and event flags
value.

+             domCode:ui::DomCode::US_Y
+          eventFlags:ui::EF_CONTROL_DOWN];
+}
+
 // Cancellation.
 
 - (void)cancelOperation:(id)sender {