Added code to fix visibility of select all option in context menu.

If context menu is appearing on some input field. Select all option
should appear only if some text is present inside input field.

BUG=395994

Review URL: https://codereview.chromium.org/402403003

git-svn-id: svn://svn.chromium.org/blink/trunk@179636 bbb929c8-8fbe-4397-9dbb-9b2b20218538