Refactor extension handling code from AppShimHost into ExtensionAppShimHandler.

apps/app_shim/app_shim_handler_mac.h

Index: apps/app_shim/app_shim_handler_mac.h
diff --git a/apps/app_shim/app_shim_handler_mac.h b/apps/app_shim/app_shim_handler_mac.h
index 6a694c0a0a3107e88e106229af8cc7bf3d4be880..507fe5f8410b055ea8f5cd26d3a3fcbb0ca6566d 100644
--- a/apps/app_shim/app_shim_handler_mac.h
+++ b/apps/app_shim/app_shim_handler_mac.h
@@ -7,6 +7,8 @@
 
 #include <string>
 
+class Profile;
+
 namespace apps {
 
 // Registrar, and interface for services that can handle interactions with OSX
@@ -18,6 +20,10 @@ class AppShimHandler {
     // Invoked when the app is closed in the browser process.
     virtual void OnAppClosed() = 0;
 
+    // Allows the handler to determine which app this host corresponds to.
+    virtual Profile* GetProfile() const = 0;
+    virtual std::string GetAppId() const = 0;
+
    protected:
     virtual ~Host() {}
   };
@@ -29,10 +35,15 @@ class AppShimHandler {
   // Remove a handler for an |app_mode_id|.
   static void RemoveHandler(const std::string& app_mode_id);
 
-  // Returns the handler registered for the given |app_mode_id|, or NULL if none
-  // is registered.
+  // Returns the handler registered for the given |app_mode_id|. If there is
+  // none registered, it returns the default handler or NULL if there is no
+  // default handler.
   static AppShimHandler* GetForAppMode(const std::string& app_mode_id);
 
+  // Sets the default handler to return when there is no app-specific handler.
+  // Setting this to NULL removes the default handler.
+  static void SetDefaultHandler(AppShimHandler* handler);
+
   // Invoked by the shim host when the shim process is launched. The handler
   // must return true if successful, or false to indicate back to the shim
   // process that it should close.