Mojo: Remove implicit scoped_refptr<T> -> T* conversions in mojo/.

R=yzshen@chromium.org

Review URL: https://codereview.chromium.org/190973008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255800 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255800