Web shell test to go back and forward.

ios/web/shell/test/web_view_matchers.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 <EarlGrey/EarlGrey.h>
+
+@interface GREYMatchers (WebViewAdditions)
+
+// Matcher for WKWebView containing |text|.
++ (id<GREYMatcher>)matcherForWebViewContainingText:(NSString*)text;
+
+#if !(GREY_DISABLE_SHORTHAND)
+
+extern "C" {
+// Shorthand for GREYMatchers::matcherForWebViewContainingText.
+GREY_EXPORT id<GREYMatcher> shell_webViewContainingText(NSString* text);
+}
+
+#endif
+
+@end