Stub out registerController() / unregisterController()

This basically hooks up the DOM bindings for navigator.registerController() up to the Blink API. Most of the actual work
will happen in chrome.

BUG=

Review URL: https://chromiumcodereview.appspot.com/23455045

git-svn-id: svn://svn.chromium.org/blink/trunk@157771 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Replace several uses of toWebCoreString() by V8TRYCATCH_FOR_V8STRINGRESOURCE() macro

Replace several uses of toWebCoreString() by V8TRYCATCH_FOR_V8STRINGRESOURCE() macro so
that we return as soon as the string conversion fails and to avoid passing a null
string to the following code.

R=haraken
BUG=

Review URL: https://chromiumcodereview.appspot.com/23526039

git-svn-id: svn://svn.chromium.org/blink/trunk@157772 bbb929c8-8fbe-4397-9dbb-9b2b20218538