Disallow redundant Bind calls.

components/sync/base/bind_to_task_runner.h

Index: components/sync/base/bind_to_task_runner.h
diff --git a/components/sync/base/bind_to_task_runner.h b/components/sync/base/bind_to_task_runner.h
index 6868b4282d17a5abec910cbe1d70e9167fb838b2..ee2972daecec5abcedb1f0b7313140d512121099 100644
--- a/components/sync/base/bind_to_task_runner.h
+++ b/components/sync/base/bind_to_task_runner.h
@@ -57,6 +57,14 @@ base::internal::PassedWrapper<ScopedVector<T>> TrampolineForward(
 template <typename Sig>
 struct BindToTaskRunnerTrampoline;
 
+template <>
+struct BindToTaskRunnerTrampoline<void()> {
+  static void Run(const scoped_refptr<base::TaskRunner>& task_runner,
+                  const base::Closure& cb) {
+    task_runner->PostTask(FROM_HERE, cb);
+  }
+};
+
 template <typename... Args>
 struct BindToTaskRunnerTrampoline<void(Args...)> {
   static void Run(const scoped_refptr<base::TaskRunner>& task_runner,