Reland r288013: First cut at "content handling" support in Mojo.

mojo/service_manager/service_loader.h

Index: mojo/service_manager/service_loader.h
diff --git a/mojo/service_manager/service_loader.h b/mojo/service_manager/service_loader.h
index 07be7d9a1bf0a314ce4f257bf045c2be2b6524af..5c44a5399ea016c9ebac598d56490512fde48777 100644
--- a/mojo/service_manager/service_loader.h
+++ b/mojo/service_manager/service_loader.h
@@ -5,8 +5,10 @@
 #ifndef MOJO_SERVICE_MANAGER_SERVICE_LOADER_H_
 #define MOJO_SERVICE_MANAGER_SERVICE_LOADER_H_
 
+#include "base/memory/ref_counted.h"
 #include "mojo/public/cpp/system/core.h"
 #include "mojo/service_manager/service_manager_export.h"
+#include "mojo/services/public/interfaces/network/url_loader.mojom.h"
 #include "url/gurl.h"
 
 namespace mojo {
@@ -23,10 +25,54 @@ class ServiceManager;
 // apps and services.
 class MOJO_SERVICE_MANAGER_EXPORT ServiceLoader {
  public:
+  class MOJO_SERVICE_MANAGER_EXPORT LoadCallbacks
+      : public base::RefCounted<LoadCallbacks> {
+   public:
+    // Register the requested application with ServiceManager. If the returned
+    // handle is valid, it should be used to implement the mojo::Application
+    // interface.
+    virtual ScopedMessagePipeHandle RegisterApplication() = 0;
+
+    // Load the requested application with a content handler.
+    virtual void LoadWithContentHandler(const GURL& content_handler_url,
+                                        URLResponsePtr response) = 0;
+   protected:
+    friend base::RefCounted<LoadCallbacks>;
+    virtual ~LoadCallbacks() {}
+  };
+
+  // Implements RegisterApplication() by returning a handle that was specified
+  // at construction time. LoadWithContentHandler() is not supported.
+  class MOJO_SERVICE_MANAGER_EXPORT SimpleLoadCallbacks : public LoadCallbacks {
+   public:
+    SimpleLoadCallbacks(ScopedMessagePipeHandle shell_handle);
+    virtual ScopedMessagePipeHandle RegisterApplication() OVERRIDE;
+    virtual void LoadWithContentHandler(const GURL& content_handler_url,
+                                        URLResponsePtr response) OVERRIDE;
+   private:
+    ScopedMessagePipeHandle shell_handle_;
+    virtual ~SimpleLoadCallbacks();
+  };
+
   virtual ~ServiceLoader() {}
-  virtual void LoadService(ServiceManager* manager,
-                           const GURL& url,
-                           ScopedMessagePipeHandle shell_handle) = 0;
+
+  // Load the application named |url|. Applications can be loaded two ways:
+  //
+  // 1. |url| can refer directly to a Mojo application. In this case, call
+  //    callbacks->RegisterApplication(). The returned handle should be used to
+  //    implement the mojo.Application interface. Note that the returned handle
+  //    can be invalid in the case where the application has already been
+  //    loaded.
+  //
+  // 2. |url| can refer to some content that can be handled by some other Mojo
+  //    application. In this case, call callbacks->LoadWithContentHandler() and
+  //    specify the URL of the application that should handle the content.
+  //    The specified application must implement the mojo.ContentHandler
+  //    interface.
+  virtual void Load(ServiceManager* service_manager,
+                    const GURL& url,
+                    scoped_refptr<LoadCallbacks> callbacks) = 0;
+
   virtual void OnServiceError(ServiceManager* manager, const GURL& url) = 0;
 
  protected: