Remove task.h and finish base::Bind() migration.

base/task.cc

Index: base/task.cc
diff --git a/base/task.cc b/base/task.cc
deleted file mode 100644
index baf4e0f6bb1f28622f78961ed8ee70c88286e4ce..0000000000000000000000000000000000000000
--- a/base/task.cc
+++ /dev/null
@@ -1,24 +0,0 @@
-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "base/task.h"
-
-namespace base {
-
-ScopedClosureRunner::ScopedClosureRunner(const Closure& closure)
-    : closure_(closure) {
-}
-
-ScopedClosureRunner::~ScopedClosureRunner() {
-  if (!closure_.is_null())
-    closure_.Run();
-}
-
-Closure ScopedClosureRunner::Release() {
-  Closure result = closure_;
-  closure_.Reset();
-  return result;
-}
-
-}  // namespace base