MacViews: Implement Full Keyboard Access.

ui/views/controls/textfield/textfield.cc

 // 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.
 
 #include "ui/views/controls/textfield/textfield.h"
 
 #include <string>
 #include <utility>
 
 #include "base/trace_event/trace_event.h"
@@ skipping 276 matching lines @@
       drop_cursor_visible_(false),
       initiating_drag_(false),
       aggregated_clicks_(0),
       drag_start_display_offset_(0),
       touch_handles_hidden_due_to_scroll_(false),
       weak_ptr_factory_(this) {
   set_context_menu_controller(this);
   set_drag_controller(this);
   GetRenderText()->SetFontList(GetDefaultFontList());
   SetBorder(std::unique_ptr<Border>(new FocusableBorder()));
+
+  // On Mac, only textfields and list controls are focusable by default. Hence

[tapted, 2016/04/20 06:05:58]

Same here. E.g. saying "only <foo>" suggests we're about to make it _not_
focusable, because we're not a <foo>. But this is a <foo>.

This probably doesn't need a comment at all. A textfield without focus is a
weird concept on any platform.

[karandeepb, 2016/05/03 02:54:13]

Done.

+  // use ALWAYS focus behavior.
   SetFocusBehavior(FocusBehavior::ALWAYS);
 
   if (ViewsDelegate::GetInstance()) {
     password_reveal_duration_ =
         ViewsDelegate::GetInstance()
             ->GetDefaultTextfieldObscuredRevealDuration();
   }
 
   // These allow BrowserView to pass edit commands from the Chrome menu to us
   // when we're focused by simply asking the FocusManager to
@@ skipping 1606 matching lines @@
     RequestFocus();
   model_->MoveCursorTo(mouse);
   if (!selection_clipboard_text.empty()) {
     model_->InsertText(selection_clipboard_text);
     UpdateAfterChange(true, true);
   }
   OnAfterUserAction();
 }
 
 }  // namespace views