mash: Replace int ShelfIDs with AppLaunchID strings.

ash/public/cpp/app_launch_id.h

 // 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.
 
 #ifndef ASH_PUBLIC_CPP_APP_LAUNCH_ID_H_
 #define ASH_PUBLIC_CPP_APP_LAUNCH_ID_H_
 
 #include <string>
 
 #include "ash/public/cpp/ash_public_export.h"
 
 namespace ash {
 
 // A unique shelf item id composed of an |app_id| and a |launch_id|.
 // |app_id| is the non-empty application id associated with a set of windows.
 // |launch_id| is passed on app launch, to support multiple shelf items per app.
 // As an example, a remote desktop client may want each remote application to
 // have its own icon.
 class ASH_PUBLIC_EXPORT AppLaunchId {
  public:
   AppLaunchId(const std::string& app_id, const std::string& launch_id);
   // Creates an AppLaunchId with an empty |launch_id|.
   explicit AppLaunchId(const std::string& app_id);
   // Empty constructor for pre-allocating.
   AppLaunchId();
   ~AppLaunchId();
 
-  AppLaunchId(const AppLaunchId& app_launch_id) = default;
-  AppLaunchId(AppLaunchId&& app_launch_id) = default;
+  AppLaunchId(const AppLaunchId& other) = default;
+  AppLaunchId(AppLaunchId&& other) = default;
   AppLaunchId& operator=(const AppLaunchId& other) = default;
+  bool operator==(const AppLaunchId& other) const;
+  bool operator!=(const AppLaunchId& other) const;
+  bool operator<(const AppLaunchId& other) const;
+
+  // Returns true if both the application id and launch id are empty.
+  bool IsEmpty() const;

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

naming question: Should this be IsValid()? Or have the comment say something
about what it means when both are empty? It's not clear from just this header
what empty is used for.

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

Hmm, it would be nice to invert the boolean, but I didn't want to claim that an
ID is "valid" simply because one or both of the strings are not empty. Validity
might seem to imply more than that. It'd change many callsites, but I'll switch
to IsValid or maybe IsViable or similar if you prefer that (left as-is for now).

[James Cook, 2017/05/04 19:45:07]

OK. Please update the comment to say that empty is often used as a null or
invalid value.

highly optional: What do you think about IsNull() vs. IsEmpty()?

[msw, 2017/05/04 20:39:07]

Done.

 
   const std::string& app_id() const { return app_id_; }
   const std::string& launch_id() const { return launch_id_; }
 
  private:
   // The application id associated with a set of windows.
   std::string app_id_;
   // An id passed on app launch, to support multiple shelf items per app.
   std::string launch_id_;
 };
 
 }  // namespace ash
 
 #endif  // ASH_PUBLIC_CPP_APP_LAUNCH_ID_H_