Support exposing Mojo services between render frames, render threads, and their respective hosts.

content/public/common/service_registry.h

+// Copyright 2014 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 CONTENT_PUBLIC_COMMON_SERVICE_REGISTRY_H_
+#define CONTENT_PUBLIC_COMMON_SERVICE_REGISTRY_H_
+
+#include <string>
+
+#include "base/callback.h"
+#include "base/strings/string_piece.h"
+#include "mojo/public/cpp/bindings/interface_ptr.h"
+#include "mojo/public/cpp/system/core.h"
+
+namespace content {
+
+// A ServiceRegistry exposes local services that have been added using
+// AddService to a paired remote ServiceRegistry and provides local access to
+// services exposed by the remote ServiceRegistry through ConnectTo.
+class ServiceRegistry {
+ public:
+  virtual ~ServiceRegistry() {}
+
+  // Make the service created by |service_factory| available to the remote

[darin (slow to review), 2014/06/12 05:27:12]

nit: Would help to clarify that the callback is run to create a new connection
to the service. The pipe handle represents that new connection.

[Sam McNally, 2014/06/12 08:56:40]

Done.

+  // InterfaceProvider.
+  template <typename Interface>
+  void AddService(const base::Callback<void(mojo::ScopedMessagePipeHandle)>

[darin (slow to review), 2014/06/12 05:27:12]

Since we know the interface here, I wonder if it might be nice to use
InterfaceRequest<Interface> here instead of mojo::ScopedMessagePipeHandle.
Perhaps it would enable callers of AddService to be more typesafe? The downside
is that you can't just pass that callback along to the virtual AddService method
:-/ Maybe that makes it not worth it.

[Sam McNally, 2014/06/12 08:56:40]

Done.

+                      service_factory) {
+    AddService(Interface::Name_, service_factory);
+  }
+  virtual void AddService(
+      const std::string& service_name,
+      const base::Callback<void(mojo::ScopedMessagePipeHandle)>
+          service_factory) = 0;
+
+  // Remove future access to the service implementing Interface. Existing
+  // connections to the service are unaffected.
+  template <typename Interface>
+  void RemoveService() {
+    RemoveService(Interface::Name_);
+  }
+  virtual void RemoveService(const std::string& service_name) = 0;
+
+  // Connect to an interface provided by the remote interface provider.
+  template <typename Interface>
+  void GetInterface(mojo::InterfacePtr<Interface>* ptr) {
+    mojo::MessagePipe pipe;
+    ptr->Bind(pipe.handle0.Pass());
+    GetInterface(Interface::Name_, pipe.handle1.Pass());
+  }
+  virtual void GetInterface(const base::StringPiece& name,
+                            mojo::ScopedMessagePipeHandle handle) = 0;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_COMMON_SERVICE_REGISTRY_H_