Add DEPS file disallowing content/public to depend back to content/.

BUG=98716


Review URL: http://codereview.chromium.org/8890075

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@114217 0039d316-1c4b-4281-b951-d872f2087c98

content/public/DEPS

+include_rules = [
+  "-content",
+
+  # This file does not belong in content/public as it should not be
+  # included directly by embedders of content/.  It must however be
+  # available to code in content/public.
+  "+content/common/content_export.h",
+  "+content/public",
+]