[Android] Add AndroidSpellChecker feature to allow for gradual rollout using finch.

components/spellcheck/renderer/spellcheck.cc

 // Copyright (c) 2012 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 "components/spellcheck/renderer/spellcheck.h"
 
 #include <stddef.h>
 #include <stdint.h>
 #include <algorithm>
 #include <utility>
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/single_thread_task_runner.h"
 #include "base/stl_util.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "build/build_config.h"
 #include "components/spellcheck/common/spellcheck_common.h"
+#include "components/spellcheck/common/spellcheck_features.h"
 #include "components/spellcheck/common/spellcheck_messages.h"
 #include "components/spellcheck/common/spellcheck_result.h"
 #include "components/spellcheck/common/spellcheck_switches.h"
 #include "components/spellcheck/renderer/spellcheck_language.h"
 #include "components/spellcheck/renderer/spellcheck_provider.h"
 #include "content/public/renderer/render_thread.h"
 #include "content/public/renderer/render_view.h"
 #include "content/public/renderer/render_view_visitor.h"
 #include "ipc/ipc_platform_file.h"
 #include "third_party/WebKit/public/platform/WebString.h"
@@ skipping 498 matching lines @@
         static_cast<WebTextDecorationType>(decoration),
         line_offset + spellcheck_result.location, spellcheck_result.length,
         replacement, spellcheck_result.hash));
   }
 
   textcheck_results->assign(results);
 }
 
 bool SpellCheck::IsSpellcheckEnabled() {
 #if defined(OS_ANDROID)
-  if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
-          spellcheck::switches::kEnableAndroidSpellChecker)) {
-    return false;
-  }
+  if (!spellcheck::IsAndroidSpellCheckFeatureEnabled()) return false;
 #endif
   return spellcheck_enabled_;
 }