Remove V8HiddenPropertyName

V8HiddenPropertyName is used as a thin wrapper for GetHiddenValue(name) and SetHiddenValue(name) in order to prefix the name with "WebCore::HiddenProperty::". This prefix is for avoiding naming conflicts with someone who sets hidden values as well. However, given that V8 binding is the only guy who sets the hidden values on DOM wrappers, there is no need to use the prefix.

- By removing the prefix, we can remove all code about V8HiddenPropertyName.

- By removing the prefix, we can slightly improve performance of GetHiddenValue() and SetHiddenValue() since we no longer need to prefix strings nor look up V8PerIsolateData to get cached, prefixed strings. (I don't know if the performance of GetHiddenValue()/SetHiddenValue() matters though.)

Given the above, this CL removes V8HiddenPropertyName.

Review URL: https://codereview.chromium.org/135843008

git-svn-id: svn://svn.chromium.org/blink/trunk@165735 bbb929c8-8fbe-4397-9dbb-9b2b20218538