Fix an "content_scipts" issue in manifest.html document

BUG=317167
TEST=pass manifest_data_source_test

Review URL: https://codereview.chromium.org/68023002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234167 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234167