Revert of Remove shell::Loader

services/shell/background/background_shell.cc

Index: services/shell/background/background_shell.cc
diff --git a/services/shell/background/background_shell.cc b/services/shell/background/background_shell.cc
index 7e16e7c14caa595742fd641dd7aff54616011669..6ce9f8a48ece47574b97a909a5dbf0565244fa10 100644
--- a/services/shell/background/background_shell.cc
+++ b/services/shell/background/background_shell.cc
@@ -15,6 +15,7 @@
 #include "mojo/message_pump/message_pump_mojo.h"
 #include "services/catalog/store.h"
 #include "services/shell/connect_params.h"
+#include "services/shell/loader.h"
 #include "services/shell/public/cpp/shell_client.h"
 #include "services/shell/public/cpp/shell_connection.h"
 #include "services/shell/shell.h"
@@ -27,6 +28,30 @@
 std::unique_ptr<base::MessagePump> CreateMessagePumpMojo() {
   return base::WrapUnique(new mojo::common::MessagePumpMojo);
 }
+
+// Used to obtain the ShellClientRequest for an application. When Loader::Load()
+// is called a callback is run with the ShellClientRequest.
+class BackgroundLoader : public Loader {
+ public:
+  using Callback = base::Callback<void(mojom::ShellClientRequest)>;
+
+  explicit BackgroundLoader(const Callback& callback) : callback_(callback) {}
+  ~BackgroundLoader() override {}
+
+  // Loader:
+  void Load(const std::string& name,
+            mojom::ShellClientRequest request) override {
+    DCHECK(!callback_.is_null());  // Callback should only be run once.
+    Callback callback = callback_;
+    callback_.Reset();
+    callback.Run(std::move(request));
+  }
+
+ private:
+  Callback callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(BackgroundLoader);
+};
 
 class MojoMessageLoop : public base::MessageLoop {
  public:
@@ -52,16 +77,20 @@
   ~MojoThread() override {}
 
   void CreateShellClientRequest(base::WaitableEvent* signal,
-                                const std::string& name,
+                                std::unique_ptr<ConnectParams> params,
                                 mojom::ShellClientRequest* request) {
     // Only valid to call this on the background thread.
     DCHECK_EQ(message_loop_, base::MessageLoop::current());
-    *request = context_->shell()->InitInstanceForEmbedder(name);
-    signal->Signal();
-  }
-
-  void Connect(std::unique_ptr<ConnectParams> params) {
+
+    // Ownership of |loader| passes to Shell.
+    const std::string name = params->target().name();
+    BackgroundLoader* loader = new BackgroundLoader(
+        base::Bind(&MojoThread::OnGotApplicationRequest, base::Unretained(this),
+                   name, signal, request));
+    context_->shell()->SetLoaderForName(base::WrapUnique(loader), name);
     context_->shell()->Connect(std::move(params));
+    // The request is asynchronously processed. When processed
+    // OnGotApplicationRequest() is called and we'll signal |signal|.
   }
 
   base::MessageLoop* message_loop() { return message_loop_; }
@@ -119,6 +148,16 @@
   }
 
  private:
+  void OnGotApplicationRequest(const std::string& name,
+                               base::WaitableEvent* signal,
+                               mojom::ShellClientRequest* request_result,
+                               mojom::ShellClientRequest actual_request) {
+    *request_result = std::move(actual_request);
+    // Trigger destruction of the loader.
+    context_->shell()->SetLoaderForName(nullptr, name);
+    signal->Signal();
+  }
+
   // We own this. It's created on the main thread, but destroyed on the
   // background thread.
   MojoMessageLoop* message_loop_ = nullptr;
@@ -154,13 +193,9 @@
   base::WaitableEvent signal(true, false);
   thread_->message_loop()->task_runner()->PostTask(
       FROM_HERE, base::Bind(&MojoThread::CreateShellClientRequest,
-                            base::Unretained(thread_.get()), &signal, name,
-                            &request));
+                            base::Unretained(thread_.get()), &signal,
+                            base::Passed(&params), &request));
   signal.Wait();
-  thread_->message_loop()->task_runner()->PostTask(
-      FROM_HERE, base::Bind(&MojoThread::Connect,
-                            base::Unretained(thread_.get()),
-                            base::Passed(&params)));
   return request;
 }