Extract shell methods from ApplicationImpl into a base class, and pass this to Initialize() instead.

mojo/services/tracing/public/cpp/tracing_impl.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 MOJO_SERVICES_TRACING_PUBLIC_CPP_TRACING_IMPL_H_
 #define MOJO_SERVICES_TRACING_PUBLIC_CPP_TRACING_IMPL_H_
 
 #include "base/macros.h"
 #include "mojo/services/tracing/public/cpp/trace_provider_impl.h"
 #include "mojo/services/tracing/public/interfaces/tracing.mojom.h"
 #include "mojo/shell/public/cpp/interface_factory.h"
 
 namespace mojo {
 
 class ApplicationConnection;
-class ApplicationImpl;
+class Shell;
 
 // Connects to mojo:tracing during your Application's Initialize() call once
 // per process.
 //
 // We need to deal with multiple ways of packaging mojo applications
 // together. We'll need to deal with packages that use the mojo.ContentHandler
 // interface to bundle several Applciations into a single physical on disk
 // mojo binary, and with those same services each in their own mojo binary.
 //
 // Have your bundle ContentHandler own a TracingImpl, and each Application own
 // a TracingImpl. In bundles, the second TracingImpl will be a no-op.
 class TracingImpl : public InterfaceFactory<tracing::TraceProvider> {
  public:
   TracingImpl();
   ~TracingImpl() override;
 
   // This connects to the tracing service and registers ourselves to provide
   // tracing data on demand.
-  void Initialize(ApplicationImpl* app);
+  void Initialize(Shell* shell, const std::string& url);
 
  private:
   // InterfaceFactory<tracing::TraceProvider> implementation.
   void Create(ApplicationConnection* connection,
               InterfaceRequest<tracing::TraceProvider> request) override;
 
   scoped_ptr<ApplicationConnection> connection_;
   TraceProviderImpl provider_impl_;
 
   DISALLOW_COPY_AND_ASSIGN(TracingImpl);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_SERVICES_TRACING_PUBLIC_CPP_TRACING_IMPL_H_