Refactor FFmpegVideoDecoder to try and generalize code common to all video decoders.

media/base/callback.h

Index: media/base/callback.h
diff --git a/media/base/callback.h b/media/base/callback.h
new file mode 100644
index 0000000000000000000000000000000000000000..553c84282ca2c643892762e4b4da754f72cd92df
--- /dev/null
+++ b/media/base/callback.h
@@ -0,0 +1,62 @@
+// Copyright (c) 2009 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.
+
+// Some basic utilities for aiding in the management of Tasks and Callbacks.
+// AutoTaskRunner, and its brother AutoCallbackRunner are the scoped_ptr
+// equivalents for callbacks.  They are useful for ensuring a callback is
+// executed and delete in the face of multiple return points in a function.
+
+#ifndef MEDIA_BASE_CALLBACK_
+#define MEDIA_BASE_CALLBACK_
+
+#include "base/scoped_ptr.h"
+#include "base/task.h"
+
+namespace media {
+
+class AutoTaskRunner {
+ public:
+  // Takes ownership of the task.
+  explicit AutoTaskRunner(Task* task)
+      : task_(task) {
+  }
+
+  ~AutoTaskRunner() {
+    if (task_.get()) {
+      task_->Run();
+    }
+  }
+
+  Task* release() { return task_.release(); }
+
+ private:
+  scoped_ptr<Task> task_;
+
+  DISALLOW_COPY_AND_ASSIGN(AutoTaskRunner);
+};
+
+class AutoCallbackRunner {
+ public:
+  // Takes ownership of the callback.
+  explicit AutoCallbackRunner(Callback0::Type* callback)
+      : callback_(callback) {
+  }
+
+  ~AutoCallbackRunner() {
+    if (callback_.get()) {
+      callback_->Run();
+    }
+  }
+
+  Callback0::Type* release() { return callback_.release(); }
+
+ private:
+  scoped_ptr<Callback0::Type> callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(AutoCallbackRunner);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_CALLBACK_