Convert Extension* to extension id in AppLaunchParams.

apps/launcher.h

Index: apps/launcher.h
diff --git a/apps/launcher.h b/apps/launcher.h
index 8da998d4cfa378e27a4c1ae3a9c2bc6065cf1248..579da0fff1948cce69c9037a985b4158bcb8b464 100644
--- a/apps/launcher.h
+++ b/apps/launcher.h
@@ -23,11 +23,11 @@ namespace apps {
 
 // Launches the platform app |extension|. Creates appropriate launch data for
 // the |command_line| fields present. |extension| and |profile| must not be
-// NULL. A NULL |command_line| means there is no launch data. If non-empty,
+// NULL. An empty |command_line| means there is no launch data. If non-empty,
 // |current_directory| is used to expand any relative paths on the command line.
 void LaunchPlatformAppWithCommandLine(Profile* profile,
                                       const extensions::Extension* extension,
-                                      const CommandLine* command_line,
+                                      const CommandLine& command_line,
                                       const base::FilePath& current_directory);
 
 // Launches the platform app |extension| by issuing an onLaunched event