Add MemoryCoordinator

components/memory_coordinator/browser/memory_state_notifier.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 "components/memory_coordinator/browser/memory_state_notifier.h"
+
+#include "base/bind.h"
+#include "base/memory/singleton.h"
+
+namespace memory_coordinator {
+
+MemoryStateNotifier::MemoryStateNotifier() {}
+
+MemoryStateNotifier::~MemoryStateNotifier() {}
+
+void MemoryStateNotifier::Notify(mojom::MemoryState state) {
+  for (auto& pair : children_) {
+    pair.second->OnStateChange(state);
+  }
+}
+
+void MemoryStateNotifier::IterateChildren(const IterateCallback& callback) {
+  for (auto& pair : children_) {
+    callback.Run(pair.second);
+  }
+}
+
+void MemoryStateNotifier::AddChild(mojom::ChildMemoryCoordinatorPtr child) {
+  int id = GetNextId();

[haraken, 2016/06/27 02:17:07]

Would you help me understand why you need an id system? (i.e., why it's not
enough to just keep the list of child coordinators)

[bashi, 2016/06/27 03:49:29]

ChildMemoryCoordinatorPtr is an alias for InterfacePtr and it doesn't support
copy and compare, so
- we can't use std::set
- when we use std::vector we need to pass the pointer of the InterfacePtr to
RemoveChild() and RemoveChild() needs to iterate the list to remove it from the
list. The same can be said to other list-like containers

I think using IDs is simple.

+  children_[id] = std::move(child);
+  children_[id].set_connection_error_handler(base::Bind(
+      &MemoryStateNotifier::RemoveChild, base::Unretained(this), id));
+}
+
+int MemoryStateNotifier::GetNextId() {
+  return ++next_id_;
+}
+
+void MemoryStateNotifier::RemoveChild(int id) {
+  children_.erase(id);
+}
+
+}  // namespace memory_coordinator