AX: AutoFill button is not accessible with VoiceOver

AX: AutoFill button is not accessible with VoiceOver
https://bugs.webkit.org/show_bug.cgi?id=145200
<rdar://problem/20507480>

Reviewed by Chris Fleizach.

Source/WebCore:

Add ARIA label and role attributes to the AutoFill button markup so that VoiceOver
can identify and interact with it.

Test: accessibility/input-auto-fill-button.html

* English.lproj/Localizable.strings: Add placeholder localized string for AutoFill button.
* html/TextFieldInputType.cpp:
(WebCore::TextFieldInputType::createAutoFillButton): Add ARIA label and role attributes.
* platform/LocalizedStrings.cpp:
(WebCore::AXAutoFillButtonText): Added; returns the localized string for the AutoFill button.
* platform/LocalizedStrings.h:
* platform/efl/LocalizedStringsEfl.cpp:
(WebCore::AXAutoFillButtonText): Ditto.
* platform/gtk/LocalizedStringsGtk.cpp:
(WebCore::AXAutoFillButtonText): Ditto.

LayoutTests:

Test that there is an accessibility element for the AutoFill button.

* accessibility/input-auto-fill-button-expected.txt: Added.
* accessibility/input-auto-fill-button.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@184645 268f45cc-cd09-0410-ab3c-d52691b4dbfc