change WebViewImpl::inputModeOfFocusedElement to return lowered string.
This string casted to WebString is compared to string such as "kana", "verbatim".

The input mode attribute is enumerated attribute [1], which should be　case-insensitive [2]. 
We had better normalize values in Blink because it's a web　standard matter.

[1]
 http://www.whatwg.org/specs/web-apps/current-work/multipage/association-of-controls-and-forms.html#attr-fe-inputmode
[2]
 http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#enumerated-attribute

In this cl we decide to use lower case.

and delete an unused test case.

BUG=244688

Review URL: https://chromiumcodereview.appspot.com/18094004

git-svn-id: svn://svn.chromium.org/blink/trunk@153609 bbb929c8-8fbe-4397-9dbb-9b2b20218538