Componentize spellcheck [1]: create component and move switches there.

components/spellcheck/common/spellcheck_switches.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 COMPONENTS_SPELLCHECK_COMMON_SPELLCHECK_SWITCHES_H_
+#define COMPONENTS_SPELLCHECK_COMMON_SPELLCHECK_SWITCHES_H_
+
+#include "build/build_config.h"
+
+namespace spellcheck {
+namespace switches {
+
+#if defined(ENABLE_SPELLCHECK)
+#if defined(OS_ANDROID)
+extern const char kEnableAndroidSpellChecker[];
+#endif  // defined(OS_ANDROID)
+extern const char kEnableSpellingFeedbackFieldTrial[];
+extern const char kSpellingServiceFeedbackIntervalSeconds[];
+extern const char kSpellingServiceFeedbackUrl[];
+#endif  // defined(ENABLE_SPELLCHECK)
+
+}  // namespace switches
+}  // namespace spellcheck
+
+#endif  // COMPONENTS_SPELLCHECK_COMMON_SPELLCHECK_SWITCHES_H_