Revert 158371 "Improve exception error messages in DOMTokenList."

Needed to allow revert of 158367, which caused major performance
regressions

BUG=299725

> Improve exception error messages in DOMTokenList.
> 
> BUG=270033
> 
> Review URL: https://chromiumcodereview.appspot.com/23609063

TBR=mkwst@chromium.org

Review URL: https://codereview.chromium.org/25011005

git-svn-id: svn://svn.chromium.org/blink/trunk@158451 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make DOMParser::parseFromString specification compliant and throw exception in error scenario.

Make DOMParser::parseFromString() allow only the supported mime-types by specification -
http://domparsing.spec.whatwg.org/#the-domparser-interface

In case of wrong mime type or mixed case mimetype as specified in the specification,
throw TypeError exception. Throwing exception can be seen implemented by FF and Opera 12.

Review URL: https://chromiumcodereview.appspot.com/24483007

git-svn-id: svn://svn.chromium.org/blink/trunk@158452 bbb929c8-8fbe-4397-9dbb-9b2b20218538