Remove usage of deprecated V8 APIs from mojo

R=mkwst@chromium.org
TBR=abarth@chromium.org
BUG=324225

Review URL: https://codereview.chromium.org/94483002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237754 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237754