chromeos: Update system_api dep to bb9b9a70.

This updates the dependency to pick up
power_manager::kPowerButtonEventSignal.

BUG=98328
TEST=synced and built successfully
TBR=satorux@chromium.org

Review URL: http://codereview.chromium.org/8889028

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@113674 0039d316-1c4b-4281-b951-d872f2087c98

tools/cros.DEPS/DEPS

@@ -7,6 +7,6 @@ deps_os = {
     "src/third_party/cros":
       Var("chromiumos_git") + "/platform/cros.git@63b0d1fd",
     "src/third_party/cros_system_api":
-      Var("chromiumos_git") + "/platform/system_api.git@bb265e37",
+      Var("chromiumos_git") + "/platform/system_api.git@bb9b9a70",
   }
 }