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

android_webview/browser/command_line_helper.cc

Index: android_webview/browser/command_line_helper.cc
diff --git a/android_webview/browser/command_line_helper.cc b/android_webview/browser/command_line_helper.cc
new file mode 100644
index 0000000000000000000000000000000000000000..6cd85a2859b421c65c0f92ffead8ea399d1d63b4
--- /dev/null
+++ b/android_webview/browser/command_line_helper.cc
@@ -0,0 +1,42 @@
+// 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.
+
+#include "android_webview/browser/command_line_helper.h"
+
+#include <vector>
+
+#include "base/command_line.h"
+#include "base/feature_list.h"
+#include "base/stl_util.h"
+#include "base/strings/string_util.h"
+#include "content/public/common/content_switches.h"
+
+using std::string;
+using std::vector;
+
+// static
+void CommandLineHelper::AddEnabledFeature(base::CommandLine& command_line,
+                                          const string& feature_name) {
+  const string enabled_features_list =
+      command_line.GetSwitchValueASCII(switches::kEnableFeatures);
+  const string disabled_features_list =
+      command_line.GetSwitchValueASCII(switches::kDisableFeatures);
+
+  if (enabled_features_list.empty() && disabled_features_list.empty()) {
+    command_line.AppendSwitchASCII(switches::kEnableFeatures, feature_name);
+    return;
+  }
+
+  vector<string> enabled_features =
+      base::FeatureList::SplitFeatureListString(enabled_features_list);
+  vector<string> disabled_features =
+      base::FeatureList::SplitFeatureListString(disabled_features_list);
+
+  if (!base::ContainsValue(enabled_features, feature_name) &&
+      !base::ContainsValue(disabled_features, feature_name)) {
+    enabled_features.push_back(feature_name);
+    command_line.AppendSwitchASCII(switches::kEnableFeatures,
+                                   base::JoinString(enabled_features, ","));
+  }
+}