mash: Replace int ShelfIDs with AppLaunchID strings.

ash/public/cpp/app_launch_id.cc

 // Copyright 2017 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 "ash/public/cpp/app_launch_id.h"
 
 #include "base/logging.h"
 
 namespace ash {
 
 AppLaunchId::AppLaunchId(const std::string& app_id,
                          const std::string& launch_id)
     : app_id_(app_id), launch_id_(launch_id) {
-  DCHECK(!app_id.empty());
+  DCHECK(launch_id.empty() || !app_id.empty()) << "launch ids require app ids.";
 }
 
-AppLaunchId::AppLaunchId(const std::string& app_id) : app_id_(app_id) {
-  DCHECK(!app_id.empty());
-}
+AppLaunchId::AppLaunchId(const std::string& app_id) : app_id_(app_id) {}

[James Cook, 2017/05/04 16:38:48]

optional: = default (and below)

[msw, 2017/05/04 19:05:56]

Doneish, it works for the empty-arg default ctor and the dtor, but not this one.
Here's the compile error: "only special member functions may be defaulted"
I also moved the "= default;" defs here from the header, per Elliot's advice.

 
 AppLaunchId::AppLaunchId() {}
 
 AppLaunchId::~AppLaunchId() {}
 
+bool AppLaunchId::operator==(const AppLaunchId& other) const {
+  return app_id_ == other.app_id_ && launch_id_ == other.launch_id_;
+}
+
+bool AppLaunchId::operator!=(const AppLaunchId& other) const {
+  return !(*this == other);
+}
+
+bool AppLaunchId::operator<(const AppLaunchId& other) const {
+  return app_id_ < other.app_id_ ||
+         (app_id_ == other.app_id_ && launch_id_ < other.launch_id_);
+}
+
+bool AppLaunchId::IsEmpty() const {
+  return app_id_.empty() && launch_id_.empty();
+}
+
 }  // namespace ash