Fix ArcBridgeBootstrap race issues.

components/arc/arc_bridge_bootstrap.h

 // Copyright 2015 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 COMPONENTS_ARC_ARC_BRIDGE_BOOTSTRAP_H_
 #define COMPONENTS_ARC_ARC_BRIDGE_BOOTSTRAP_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/sequenced_task_runner.h"
 #include "base/single_thread_task_runner.h"
 #include "components/arc/arc_bridge_service.h"
 #include "components/arc/common/arc_bridge.mojom.h"
 
 namespace arc {
 
 // Starts the ARC instance and bootstraps the bridge connection.
 // Clients should implement the Delegate to be notified upon communications
 // being available.
+// The instance can be safely removed 1) before Start() is called, or 2) after
+// OnStopped() is called.
+// The number of instances must be at most one. Otherwise, ARC instances will
+// conflict.
+// TODO(hidehiko): This class manages more than "bootstrap" procedure now.
+// Rename this to ArcSession.
 class ArcBridgeBootstrap {
  public:
+  // TODO(hidehiko): Switch to Observer style, which fits more for this design.
   class Delegate {
    public:
     // Called when the connection with ARC instance has been established.
+    // TODO(hidehiko): Moving ArcBridgeHost to the ArcBridgeBootstrapImpl
+    // so that this can be replaced by OnReady() simply.
     virtual void OnConnectionEstablished(
         mojom::ArcBridgeInstancePtr instance_ptr) = 0;
 
-    // Called when ARC instance is stopped.
+    // Called when ARC instance is stopped. This is called exactly once
+    // per instance which is Start()ed.
     virtual void OnStopped(ArcBridgeService::StopReason reason) = 0;
   };
 
   // Creates a default instance of ArcBridgeBootstrap.
   static std::unique_ptr<ArcBridgeBootstrap> Create();
   virtual ~ArcBridgeBootstrap() = default;
 
   // This must be called before calling Start() or Stop(). |delegate| is owned
   // by the caller and must outlive this instance.
   void set_delegate(Delegate* delegate) { delegate_ = delegate; }
 
   // Starts and bootstraps a connection with the instance. The Delegate's
   // OnConnectionEstablished() will be called if the bootstrapping is
   // successful, or OnStopped() if it is not.
+  // Start() should not be called twice or more.
   virtual void Start() = 0;
 
-  // Stops the currently-running instance.
+  // Requests to stop the currently-running instance.
+  // The completion is notified via OnStopped() of the Delegate.
   virtual void Stop() = 0;
 
  protected:
   ArcBridgeBootstrap() = default;
 
   // Owned by the caller.
   Delegate* delegate_ = nullptr;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ArcBridgeBootstrap);
 };
 
 }  // namespace arc
 
 #endif  // COMPONENTS_ARC_ARC_BRIDGE_BOOTSTRAP_H_