https://bugs.webkit.org/show_bug.cgi?id=95542

Reviewed by Kent Tamura.

This patch changes width of AM/PM field of multiple field time input
UI fixed as maximum width of labels or "--".

This patch affects ports which enable both ENABLE_INPUT_TYPE_TIME and
ENABLE_INPUT_TYPE_TIME_MULTIPLE_FIELDS.

No new tests. Once multiple field time input UI uses "lang" HTML
attribute to take time format, we can write a test for this patch.

* css/html.css:
(input::-webkit-datetime-edit-ampm-field): Added "display" property to "inline-block" for setting width.
Added "text-align" property to "center".
* html/shadow/DateTimeSymbolicFieldElement.cpp:
(WebCore::DateTimeSymbolicFieldElement::DateTimeSymbolicFieldElement): Changed to call setHasCustomCallback().
(WebCore::DateTimeSymbolicFieldElement::customStyleForRenderer): Added for setting field with from maximum width of labels.
* html/shadow/DateTimeSymbolicFieldElement.h:
(WebCore::DateTimeSymbolicFieldElement::visibleEmptyValue): Added for using visible empty value in customStyleForRenderer() and visibleValue().
(WebCore::DateTimeSymbolicFieldElement::visibleValue): Changed to call visibleEmptyValue() instead of using literal "--".
(DateTimeSymbolicFieldElement): Added a declaration of customStyleForRenderer().

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@127398 268f45cc-cd09-0410-ab3c-d52691b4dbfc