AU: Restrict URL/version change over D-Bus to non-official builds only.

BUG=7159
TEST=unit tests, test on device

Change-Id: I7dd6293d3e61db123b2be2f1e3ee283fcb5ba968

Review URL: http://codereview.chromium.org/3965001
diff --git a/utils.cc b/utils.cc
index c8a4da6..162fe7b 100644
--- a/utils.cc
+++ b/utils.cc
@@ -39,14 +39,10 @@
 namespace utils {
 
 static const char kOOBECompletedMarker[] = "/home/chronos/.oobe_completed";
+static const char kDevImageMarker[] = "/root/.dev_mode";
 
 bool IsOfficialBuild() {
-  OmahaRequestDeviceParams params;
-  if (!params.Init("", "")) {
-    return true;
-  }
-  return params.app_track != "buildbot-build" &&
-      params.app_track != "developer-build";
+  return !file_util::PathExists(FilePath(kDevImageMarker));
 }
 
 bool IsOOBEComplete() {