Teach the mojo_shell --trace-startup flag to gather data from services

shell/context.h

 // Copyright 2013 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 SHELL_CONTEXT_H_
 #define SHELL_CONTEXT_H_
 
 #include <string>
 
 #include "base/macros.h"
 #include "mojo/edk/embedder/process_delegate.h"
 #include "shell/application_manager/application_manager.h"
 #include "shell/task_runners.h"
 #include "shell/url_resolver.h"
 
 namespace shell {
-
-class NativeApplicationLoader;
+class Tracer;
 
 // The "global" context for the shell's main process.
 class Context : public ApplicationManager::Delegate,
                 public mojo::embedder::ProcessDelegate {
  public:
-  Context();
+  explicit Context(Tracer* tracer = nullptr);
   ~Context() override;
 
   static void EnsureEmbedderIsInitialized();
 
   // Point to the directory containing installed services, such as the network
   // service. By default this directory is used as the base URL for resolving
   // unknown mojo: URLs. The network service will be loaded from this directory,
   // even when the base URL for unknown mojo: URLs is overridden.
   void SetShellFileRoot(const base::FilePath& path);
 
@@ skipping 37 matching lines @@
 
   // ApplicationManager::Delegate overrides.
   GURL ResolveURL(const GURL& url) override;
   GURL ResolveMappings(const GURL& url) override;
 
   // ProcessDelegate implementation.
   void OnShutdownComplete() override;
 
   void OnApplicationEnd(const GURL& url);
 
+  Tracer* const tracer_;
   ApplicationManager application_manager_;
   URLResolver url_resolver_;
 
   base::FilePath mojo_shell_child_path_;
   scoped_ptr<TaskRunners> task_runners_;
 
   std::set<GURL> app_urls_;
   GURL shell_file_root_;
   GURL command_line_cwd_;
 
   DISALLOW_COPY_AND_ASSIGN(Context);
 };
 
 }  // namespace shell
 
 #endif  // SHELL_CONTEXT_H_