Create ChromeEarlGrey waitForWebViewContainingText.

ios/web/public/test/web_view_content_test_util.mm

+// Copyright 2017 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/test/web_view_content_test_util.h"
+
+#import <Foundation/Foundation.h>
+
+#import "ios/web/public/test/web_view_interaction_test_util.h"
+
+namespace {
+// Script that returns document.body as a string.
+char kGetDocumentBodyJavaScript[] =
+    "document.body ? document.body.textContent : null";
+}
+
+namespace web {
+namespace test {
+
+bool IsWebViewContainingText(web::WebState* web_state,
+                             const std::string& text) {
+  std::unique_ptr<base::Value> value =
+      web::test::ExecuteJavaScript(web_state, kGetDocumentBodyJavaScript);
+  std::string body;
+  if (value && value->GetAsString(&body)) {
+    return body.find(text) != std::string::npos;
+  }
+  return false;
+}
+
+}  // namespace test
+}  // namespace web