Improve exception error messages in DOMTokenList.

BUG=270033

Review URL: https://chromiumcodereview.appspot.com/23609063

git-svn-id: svn://svn.chromium.org/blink/trunk@158371 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Cleanup: Move form-related localized string functions from LocalizedStrings to Locale.

I found fileButtonNoFilesSelectedLabel() and fileButtonNoFileSelectedLabel()
requested an identical string. This patch removes some condition checks for
HTMLInputElement::multiple().

BUG=298020
TEST=none; no behavior changes.

Review URL: https://chromiumcodereview.appspot.com/24723002

git-svn-id: svn://svn.chromium.org/blink/trunk@158372 bbb929c8-8fbe-4397-9dbb-9b2b20218538