Separate render-specific code in InputType::attach.

Separate renderer-specific code in InputType::attach.

Introduce new function InputType::countUsage, and move UseCounter code to
it. InputType::attach implementations have only renderer-specific code.

This is a preparation to support author Shadow DOM for INPUT element.

BUG=274205
TEST=none; no behavior changes

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=156380

[keishi, 2013-08-20 08:19:51]

lgtm

[commit-bot: I haz the power, 2013-08-20 08:46:50]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tkent@chromium.org/23330003/1

[commit-bot: I haz the power, 2013-08-20 08:51:04]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tkent@chromium.org/23330003/1

[commit-bot: I haz the power, 2013-08-20 09:11:24]

Change committed as 156380