Add ability to submit a form using javascript.

ios/web/public/test/web_view_interaction_test_util.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/web/public/web_state/web_state.h"
 
 #include <string>
 
 namespace web {
 namespace test {
 
 // Returns whether the element with |element_id| in the passed |web_state| has
 // been tapped using a JavaScript click() event.
 bool TapWebViewElementWithId(web::WebState* web_state,
                              const std::string& element_id);
 
 // Returns whether the element with |element_id| in the passed |web_state| has
 // been focused using a JavaScript focus() event.
 bool FocusWebViewElementWithId(web::WebState* web_state,
                                const std::string& element_id);
 
+// Returns whether the form with |form_id| in the passed |web_state| has been
+// submitted using a JavaScript submit() event.
+bool SubmitWebViewFormWithId(web::WebState* web_state,
+                             const std::string& form_id);
 }  // namespace test
 }  // namespace web