Do not make a subclass of Text only to disable selection.

We can avoid text selection by adding -webkit-user-select:none to button input
elements.

We udpate some rendering tests because of slight text color differences and
margin selection paint difference. They are acceptable because they are very
minor differences.

BUG=265699
TEST=Covered by existing tests.

Review URL: https://codereview.chromium.org/103763002

git-svn-id: svn://svn.chromium.org/blink/trunk@163162 bbb929c8-8fbe-4397-9dbb-9b2b20218538