Use a WebURL type for url parameter in registerProtocolHandler()

The registerProtocolHandler() of WebViewClient starts to use WebURL type for parameters related to url. Thus,
content layer also needs to use WebURL parameter by the change.

BUG=N/A

Review URL: https://codereview.chromium.org/143023002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246326 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246326