Revert of Use a token to initialise ChannelMojo and MojoApplication everywhere.

content/browser/mojo/mojo_application_host.h

Index: content/browser/mojo/mojo_application_host.h
diff --git a/content/browser/mojo/mojo_application_host.h b/content/browser/mojo/mojo_application_host.h
index b1bc026cfdc93dfed3504b9b1fd4b1e761a1a539..50fdfdf63fb4709259ff03046bb3cbb8fb9c6dc0 100644
--- a/content/browser/mojo/mojo_application_host.h
+++ b/content/browser/mojo/mojo_application_host.h
@@ -9,9 +9,13 @@
 #include <string>
 
 #include "base/macros.h"
+#include "base/process/process_handle.h"
 #include "build/build_config.h"
 #include "content/common/application_setup.mojom.h"
+#include "content/common/mojo/channel_init.h"
 #include "content/common/mojo/service_registry_impl.h"
+#include "mojo/edk/embedder/scoped_platform_handle.h"
+#include "mojo/public/cpp/system/message_pipe.h"
 
 #if defined(OS_ANDROID)
 #include "content/public/browser/android/service_registry_android.h"
@@ -24,18 +28,24 @@
 namespace content {
 
 // MojoApplicationHost represents the code needed on the browser side to setup
-// a child process as a Mojo application. The child process should use the token
-// from GetToken() to initialize its MojoApplication. MojoApplicationHost makes
-// the ServiceRegistry interface available so that child-provided services can
-// be invoked.
+// a child process as a Mojo application via Chrome IPC. The child process
+// should use MojoApplication to handle messages generated by an instance of
+// MojoApplicationHost. MojoApplicationHost makes the ServiceRegistry interface
+// available so that child-provided services can be invoked.
 class CONTENT_EXPORT MojoApplicationHost {
  public:
   MojoApplicationHost();
   ~MojoApplicationHost();
 
-  // Returns a token to pass to the child process to initialize its
-  // MojoApplication.
-  const std::string& GetToken() { return token_; }
+  // Two-phase initialization:
+  //  1- Init makes service_registry() available synchronously.
+  //  2- Activate establishes the actual connection to the peer process.
+  bool Init();
+  void Activate(IPC::Sender* sender, base::ProcessHandle process_handle);
+
+  // Use a shared token to initialize the application. Returns a token to pass
+  // to the child process.
+  std::string InitWithToken();
 
   ServiceRegistry* service_registry() { return &service_registry_; }
 
@@ -45,11 +55,19 @@
   }
 #endif
 
+  void OverrideIOTaskRunnerForTest(
+      scoped_refptr<base::TaskRunner> io_task_runner);
+
  private:
-  const std::string token_;
+  ChannelInit channel_init_;
+  mojo::edk::ScopedPlatformHandle client_handle_;
+
+  bool did_activate_;
 
   std::unique_ptr<mojom::ApplicationSetup> application_setup_;
   ServiceRegistryImpl service_registry_;
+
+  scoped_refptr<base::TaskRunner> io_task_runner_override_;
 
 #if defined(OS_ANDROID)
   std::unique_ptr<ServiceRegistryAndroid> service_registry_android_;