Revert of Deletes mojo::Callback

mojo/public/cpp/bindings/tests/bind_task_runner_unittest.cc

Index: mojo/public/cpp/bindings/tests/bind_task_runner_unittest.cc
diff --git a/mojo/public/cpp/bindings/tests/bind_task_runner_unittest.cc b/mojo/public/cpp/bindings/tests/bind_task_runner_unittest.cc
index dab64f012d16f86364bfc529f6493481b877f1be..7cb782db3562380912f4162102b167aec10392ab 100644
--- a/mojo/public/cpp/bindings/tests/bind_task_runner_unittest.cc
+++ b/mojo/public/cpp/bindings/tests/bind_task_runner_unittest.cc
@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 #include "base/bind.h"
-#include "base/callback.h"
 #include "base/message_loop/message_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/lock.h"
@@ -125,7 +124,7 @@
 
   ~IntegerSenderImpl() override {}
 
-  using EchoHandler = base::Callback<void(int32_t, const EchoCallback&)>;
+  using EchoHandler = Callback<void(int32_t, const EchoCallback&)>;
 
   void set_echo_handler(const EchoHandler& handler) { echo_handler_ = handler; }
 
@@ -158,7 +157,7 @@
 
   ~IntegerSenderConnectionImpl() override {}
 
-  void set_get_sender_notification(const base::Closure& notification) {
+  void set_get_sender_notification(const Closure& notification) {
     get_sender_notification_ = notification;
   }
   void GetSender(IntegerSenderAssociatedRequest sender) override {
@@ -178,7 +177,7 @@
   Binding<IntegerSenderConnection> binding_;
   std::unique_ptr<SenderType> sender_impl_;
   scoped_refptr<base::SingleThreadTaskRunner> sender_runner_;
-  base::Closure get_sender_notification_;
+  Closure get_sender_notification_;
 };
 
 class BindTaskRunnerTest : public testing::Test {