KeyedService Providers for ChromeOS (Ash)

This directory implements "Provider" classes that bridge Chrome's KeyedService instances with OS-level components in ChromeOS (Ash).

Important: Design Alternatives (Read First)

Using the Provider pattern should be considered a last resort. Before adding a new provider, evaluate whether one of the following preferred design patterns can be applied:

1. Depend on OS Components Directly

   If the required data or behavior is already available elsewhere in the OS, prefer depending on that component directly instead of reaching into a Chrome KeyedService.

2. Inject via Constructor

   If the client class is scoped to a specific User (or Profile), pass the service dependency directly through its constructor and retain a pointer or reference in a member variable.

3. Remove KeyedService Abstraction

   If the service is used exclusively on ChromeOS, consider removing KeyedService entirely. Instead, initialize the service directly during user session startup.

When to Use a Provider

A dedicated Provider class (as described below) is appropriate only when none of the alternatives apply—for example:

• The OS component must handle multiple concurrent user sessions within a single process.

• The component relies on a KeyedService shared across multiple platforms for maintainability.

Provider Architecture & Implementation

A Provider consists of three main components:

1. Provider Interface

• Location: Must reside under //chromeos/ash/ (not under //chrome/browser/**/ash).

• Structure:

class FooProvider {
 public:
  virtual ~FooProvider() = default;

  // Returns the global instance of the provider.
  static FooProvider& Get();

  // Returns the Foo KeyedService for the User with the given `account_id`.
  // Returns nullptr if the service is unavailable or cannot be created.
  virtual FooKeyedService* Find(const AccountId& account_id) = 0;
};

2. Provider Implementation

• Location: Resides in this directory.

• Behavior: Implements the Provider interface. Find() acts as a thin wrapper around the corresponding KeyedServiceFactory API, converting the AccountId to a BrowserContext / Profile.

FooKeyedService* FooProviderImpl::Find(const AccountId& account_id) {
  return FooKeyedServiceFactory::GetForBrowserContext(
      ash::BrowserContextHelper::Get()->GetBrowserContextByAccountId(account_id));
}

3. Lifecycle Management

• The Provider instance is instantiated and managed by ChromeBrowserMainPartsAsh.

• Lifetime: FooProviderImpl outlives individual Profile instances.