Add --keyboard-usability-test flag and always show keyboard unless manually hide

ui/keyboard/keyboard_switches.h

 // Copyright (c) 2013 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.
 
 #ifndef UI_KEYBOARD_KEYBOARD_SWITCHES_H_
 #define UI_KEYBOARD_KEYBOARD_SWITCHES_H_
 
 #include "ui/keyboard/keyboard_export.h"
 
 namespace keyboard {
 namespace switches {
 
 // Enables the virtual keyboard.
 KEYBOARD_EXPORT extern const char kEnableVirtualKeyboard[];
 
+// Enables the keyboard usability test.
+KEYBOARD_EXPORT extern const char kKeyboardUsabilityTest[];

[sadrul, 2013/10/23 14:01:49]

Shouldn't need to export (since it's not used outside of this component)

[bshe, 2013/10/23 17:08:43]

The reason I use EXPORT is this flag is expected to be used in ash just like
kEnableVirtualKeyboard. So I added the export here.  

On 2013/10/23 14:01:49, sadrul wrote:

[sadrul, 2013/10/23 17:45:06]

Where would you use this ash? This specific behaviour should be tested in
keyboard_unittest, and that test would add this flag to the CommandLine in the
test SetUp.

On 2013/10/23 17:08:43, bshe wrote:

[bshe, 2013/10/24 00:23:36]

It will be used to enable a special display mode(not implemented yet) in display
manager in ash. I will add a unit test here to make sure that keyboard always
show when flag is set.

On 2013/10/23 17:45:06, sadrul wrote:

+
 }  // namespace switches
 }  // namespace keyboard
 
 #endif  //  UI_KEYBOARD_KEYBOARD_SWITCHES_H_