mash: Replace int ShelfIDs with AppLaunchID strings.

ash/public/cpp/app_launch_id.cc

Index: ash/public/cpp/app_launch_id.cc
diff --git a/ash/public/cpp/app_launch_id.cc b/ash/public/cpp/app_launch_id.cc
index fc437c3afe5deb63f1808241b80a8cf0d23f7f13..7293d183a3b9ee6ceb756a6a3ddc16c2ffc2ca6d 100644
--- a/ash/public/cpp/app_launch_id.cc
+++ b/ash/public/cpp/app_launch_id.cc
@@ -10,16 +10,37 @@ 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());
+    : app_id(app_id), launch_id(launch_id) {
+  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) {}
+
+AppLaunchId::AppLaunchId() = default;
+
+AppLaunchId::~AppLaunchId() = default;
+
+AppLaunchId::AppLaunchId(const AppLaunchId& other) = default;
+
+AppLaunchId::AppLaunchId(AppLaunchId&& other) = default;
+
+AppLaunchId& AppLaunchId::operator=(const AppLaunchId& other) = default;
+
+bool AppLaunchId::operator==(const AppLaunchId& other) const {
+  return app_id == other.app_id && launch_id == other.launch_id;
 }
 
-AppLaunchId::AppLaunchId() {}
+bool AppLaunchId::operator!=(const AppLaunchId& other) const {
+  return !(*this == other);
+}
 
-AppLaunchId::~AppLaunchId() {}
+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::IsNull() const {
+  return app_id.empty() && launch_id.empty();
+}
 
 }  // namespace ash