Added a trivial fault tolerance JS module with a trivial test suite.

services/sync/modules/faultTolerance.js

@@ -0,0 +1,18 @@
+const EXPORTED_SYMBOLS = ["FaultTolerance"];
+
+FaultTolerance = {
+  get Service() {
+    if (!this._Service)
+      this._Service = new FaultToleranceService();
+    return this._Service;
+  }
+}
+
+function FaultToleranceService() {
+}
+
+FaultToleranceService.prototype = {
+  processMessage: function FTApp_doAppend(message) {
+    dump(message);
+  }
+};

services/sync/tests/unit/test_fault_tolerance.js

@@ -0,0 +1,7 @@
+function run_test() {
+  Components.utils.import("resource://weave/faultTolerance.js");
+
+  // Just make sure the getter works and the service is a singleton.
+  FaultTolerance.Service._testProperty = "hi";
+  do_check_eq(FaultTolerance.Service._testProperty, "hi");
+}