Revert of Remove shell::Loader

services/shell/shell.h

Index: services/shell/shell.h
diff --git a/services/shell/shell.h b/services/shell/shell.h
index f336025f562ea9efaf3d89aa95a8aecad586e669..fc17adf4cbf67a278b82f18355027e2f363f3d92 100644
--- a/services/shell/shell.h
+++ b/services/shell/shell.h
@@ -14,6 +14,7 @@
 #include "mojo/public/cpp/bindings/binding_set.h"
 #include "mojo/public/cpp/bindings/interface_ptr_set.h"
 #include "services/shell/connect_params.h"
+#include "services/shell/loader.h"
 #include "services/shell/native_runner.h"
 #include "services/shell/public/cpp/capabilities.h"
 #include "services/shell/public/cpp/identity.h"
@@ -53,7 +54,8 @@
   // implementations of NativeRunner, e.g. for in or out-of-process execution.
   // See native_runner.h and RunNativeApplication().
   // |file_task_runner| provides access to a thread to perform file copy
-  // operations on.
+  // operations on. This may be null only in testing environments where
+  // applications are loaded via Loader implementations.
   Shell(std::unique_ptr<NativeRunnerFactory> native_runner_factory,
         mojom::ShellClientPtr catalog);
   ~Shell() override;
@@ -72,6 +74,15 @@
   // the Shell's embedder to register itself with the shell. This must only be
   // called once.
   mojom::ShellClientRequest InitInstanceForEmbedder(const std::string& name);
+
+  // Sets the default Loader to be used if not overridden by SetLoaderForName().
+  void set_default_loader(std::unique_ptr<Loader> loader) {
+    default_loader_ = std::move(loader);
+  }
+
+  // Sets a Loader to be used for a specific name.
+  void SetLoaderForName(std::unique_ptr<Loader> loader,
+                        const std::string& name);
 
  private:
   class Instance;
@@ -136,9 +147,23 @@
                          mojom::ShellClientPtr client,
                          mojom::ResolveResultPtr result);
 
+  // Tries to load |target| with an Loader. Returns true if one was registered
+  // and it was loaded, in which case |request| is taken.
+  bool LoadWithLoader(const Identity& target,
+                      mojom::ShellClientRequest* request);
+
+  // Returns the appropriate loader for |name|, or the default loader if there
+  // is no loader configured for the name.
+  Loader* GetLoaderForName(const std::string& name);
+
   base::WeakPtr<Shell> GetWeakPtr();
 
   void CleanupRunner(NativeRunner* runner);
+
+  // Loader management.
+  // Loaders are chosen in the order they are listed here.
+  std::map<std::string, Loader*> name_to_loader_;
+  std::unique_ptr<Loader> default_loader_;
 
   std::map<Identity, Instance*> identity_to_instance_;