[chromedriver] Allow commands to be async.

chrome/test/chromedriver/command.h

Index: chrome/test/chromedriver/command.h
diff --git a/chrome/test/chromedriver/command.h b/chrome/test/chromedriver/command.h
index 6654694af5e14bb8bbeb6dba3394578f9c853786..e57a5f2ff0a9da08d0cc9e8e4f925693a00a4cd1 100644
--- a/chrome/test/chromedriver/command.h
+++ b/chrome/test/chromedriver/command.h
@@ -17,10 +17,14 @@ class Value;
 
 class Status;
 
-typedef base::Callback<Status(
+typedef base::Callback<void(
+    const Status&,
+    scoped_ptr<base::Value>,
+    const std::string&)> CommandCallback;
+
+typedef base::Callback<void(
     const base::DictionaryValue&,
     const std::string&,
-    scoped_ptr<base::Value>*,
-    std::string*)> Command;
+    const CommandCallback&)> Command;
 
 #endif  // CHROME_TEST_CHROMEDRIVER_COMMAND_H_