mash: Serialize ShelfIDs for property conversion and transport.

ash/public/cpp/shelf_types.h

Index: ash/public/cpp/shelf_types.h
diff --git a/ash/public/cpp/shelf_types.h b/ash/public/cpp/shelf_types.h
index a198dfa94601c8962f0120268bbd662ac8a9efea..1ccd5099e2ca4a46946099d4a7eabde8f384df17 100644
--- a/ash/public/cpp/shelf_types.h
+++ b/ash/public/cpp/shelf_types.h
@@ -138,8 +138,8 @@ enum ShelfItemStatus {
 // As an example, a remote desktop client may want each remote application to
 // have its own icon.
 struct ASH_PUBLIC_EXPORT ShelfID {
-  ShelfID(const std::string& app_id = std::string(),
-          const std::string& launch_id = std::string());
+  explicit ShelfID(const std::string& app_id = std::string(),
+                   const std::string& launch_id = std::string());
   ~ShelfID();
 
   ShelfID(const ShelfID& other);
@@ -153,6 +153,12 @@ struct ASH_PUBLIC_EXPORT ShelfID {
   // This is often used to determine if the id is invalid.
   bool IsNull() const;
 
+  // Functions to [de]serialize ids as a string for window property usage, etc.
+  // Serialization appends ids with a delimeter that must not be used in ids.
+  // Deserialization returns an empty/null/default id for a null string input.
+  std::string Serialize() const;
+  static ShelfID Deserialize(const std::string* string);
+
   // 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.