mojo: Add ExistingThreadLoader.

content/common/mojo/existing_thread_loader.h

Index: content/common/mojo/existing_thread_loader.h
diff --git a/content/common/mojo/existing_thread_loader.h b/content/common/mojo/existing_thread_loader.h
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+++ b/content/common/mojo/existing_thread_loader.h
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+// Copyright 2016 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_COMMON_MOJO_EXISTING_THREAD_LOADER_H_
+#define CONTENT_COMMON_MOJO_EXISTING_THREAD_LOADER_H_
+
+#include <vector>
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "mojo/shell/loader.h"
+#include "mojo/shell/public/cpp/shell_client.h"
+#include "mojo/shell/public/cpp/shell_connection.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+}
+
+namespace content {
+
+// A Loader which loads a single type of app from a mojo::ShellClientFactory on
+// an existing thread.
+class ExistingThreadLoader : public mojo::shell::Loader {
+ public:
+  using ApplicationFactory = base::Callback<scoped_ptr<mojo::ShellClient>()>;
+
+  ExistingThreadLoader(const ApplicationFactory& factory,
+                       scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+  ~ExistingThreadLoader() override;
+
+  // mojo::shell::Loader:
+  void Load(const std::string& name,
+            mojo::shell::mojom::ShellClientRequest request) override;
+
+ private:
+  void LoadOnTaskRunner(const std::string& name,
+                        mojo::shell::mojom::ShellClientRequest request);
+
+  // The factory used to create new instances of the shell client. This is
+  // called exactly once since all connections share a single client.
+  ApplicationFactory factory_;
+
+  // TaskRunner where the |shell_client_| is running on.
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  // Our shared shell client, passed to each connection.
+  scoped_ptr<mojo::ShellClient> shell_client_;
+
+  std::vector<scoped_ptr<mojo::ShellConnection>> connections_;
+
+  base::WeakPtrFactory<ExistingThreadLoader> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(ExistingThreadLoader);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_COMMON_MOJO_EXISTING_THREAD_LOADER_H_