[WIP] - trying out some state machine ideas.

media/base/state_machine.cc

+// Copyright 2016 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 "media/base/state_machine.h"
+
+namespace media {
+
+StateMachine::StateMachine() : owner_(nullptr) {}
+
+StateMachine::~StateMachine() {
+  for (scoped_refptr<State> state : states_)
+    state->UnregisterClient(this);
+}
+
+void StateMachine::SetOwner(Owner* owner) {
+  owner_ = owner;
+}
+
+void StateMachine::OnStateChanged() {
+  DCHECK(owner_);
+  owner_->RequestRun(this);
+}
+
+void StateMachine::UsingState(scoped_refptr<State> state) {
+  // TODO(liberato): check for duplicates.  Not sure why set doesn't work,
+  // since it seems like there should be a default hash defined for refptr.
+  // maybe define one if not, but probably i just forgot to tell the set
+  // about it.
+  state->RegisterClient(this);
+  states_.push_back(state);
+}
+
+}  // namespace media