[ios] Implemented -[ShellEarlGrey loadURL:].

ios/web/public/test/earl_grey/js_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.
+
+#ifndef IOS_WEB_PUBLIC_TEST_EARL_GREY_JS_TEST_UTIL_H_
+#define IOS_WEB_PUBLIC_TEST_EARL_GREY_JS_TEST_UTIL_H_
+
+#import <Foundation/Foundation.h>
+
+#import "ios/web/public/web_state/web_state.h"
+
+namespace web {
+
+// Waits until the Window ID has been injected and the page is thus ready to
+// respond to JavaScript injection. Fails with a GREYAssert on timeout or if
+// unrecoverable error (such as no web view) occurs.
+void WaitUntilWindowIdInjected(WebState* web_state);
+
+// Executes |javascript| on the given |web_state|, and waits until execution is
+// completed. If |out_error| is not nil, it is set to the error resulting from
+// the execution, if one occurs. The return value is the result of the
+// JavaScript execution. If the script execution is timed out, then this method
+// fails with a GREYAssert.
+id ExecuteJavaScript(WebState* web_state,
+                     NSString* javascript,
+                     NSError** out_error);
+
+}  // namespace web
+
+#endif  // IOS_WEB_PUBLIC_TEST_EARL_GREY_JS_TEST_UTIL_H_