Add LauncherIconObserver.

ash/test/test_shell_delegate.cc

Index: ash/test/test_shell_delegate.cc
diff --git a/ash/test/test_shell_delegate.cc b/ash/test/test_shell_delegate.cc
index dfb111201ece2b30e411ee59355a99b54c9be99a..d24d34b1c46d9abdfca53e18a060ee9aede8302a 100644
--- a/ash/test/test_shell_delegate.cc
+++ b/ash/test/test_shell_delegate.cc
@@ -9,6 +9,7 @@
 #include "ash/screenshot_delegate.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
+#include "ash/test/test_launcher_delegate.h"
 #include "grit/ui_resources.h"
 #include "ui/aura/window.h"
 
@@ -58,7 +59,7 @@ void TestShellDelegate::StartPartialScreenshot(
 
 LauncherDelegate* TestShellDelegate::CreateLauncherDelegate(
     ash::LauncherModel* model) {
-  return NULL;
+  return new TestLauncherDelegate(model);
 }
 
 SystemTrayDelegate* TestShellDelegate::CreateSystemTrayDelegate(