chrome: Cleanup class/struct forward declarations

chrome/browser/extensions/extension_function_test_utils.h

Index: chrome/browser/extensions/extension_function_test_utils.h
diff --git a/chrome/browser/extensions/extension_function_test_utils.h b/chrome/browser/extensions/extension_function_test_utils.h
index 230d739768dd8eaf1cfb78c43e76dccd2c01368f..c1ba0cd37223829185396d8e7fd721d3867b420a 100644
--- a/chrome/browser/extensions/extension_function_test_utils.h
+++ b/chrome/browser/extensions/extension_function_test_utils.h
@@ -19,10 +19,6 @@ class DictionaryValue;
 class ListValue;
 }
 
-namespace extensions {
-class Extension;
-}
-
 // TODO(ckehoe): Accept args as std::unique_ptr<base::Value>,
 // and migrate existing users to the new API.
 // This file is DEPRECATED. New tests should use the versions in