[Android WebView] Add functionality to enable features and enable the spellcheck feature.

android_webview/browser/command_line_helper.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 ANDROID_WEBVIEW_BROWSER_COMMAND_LINE_HELPER_H_
+#define ANDROID_WEBVIEW_BROWSER_COMMAND_LINE_HELPER_H_
+
+#include <string>
+
+namespace base {
+class CommandLine;
+}  // namespace base
+
+class CommandLineHelper {
+ public:
+  // Add a feature to the --enabled-features list, but only if it's not
+  // already enabled or disabled.
+  static void AddEnabledFeature(base::CommandLine& command_line,
+                                const std::string& feature_name);
+
+ private:
+  CommandLineHelper();
+};
+
+#endif  // ANDROID_WEBVIEW_BROWSER_COMMAND_LINE_HELPER_H_