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

components/spellcheck/common/spellcheck_features.h

Index: components/spellcheck/common/spellcheck_features.h
diff --git a/components/spellcheck/common/spellcheck_features.h b/components/spellcheck/common/spellcheck_features.h
new file mode 100644
index 0000000000000000000000000000000000000000..ba0e2f2f8b435fbef948ed3f170cbf870433226b
--- /dev/null
+++ b/components/spellcheck/common/spellcheck_features.h
@@ -0,0 +1,21 @@
+// 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_FEATURES_H_
+#define COMPONENTS_SPELLCHECK_COMMON_SPELLCHECK_FEATURES_H_
+
+#include "base/feature_list.h"
+
+namespace spellcheck {
+
+#if defined(ENABLE_SPELLCHECK) && defined(OS_ANDROID)
+extern const base::Feature kAndroidSpellChecker;
+extern const base::Feature kAndroidSpellCheckerNonLowEnd;
+
+bool IsAndroidSpellCheckFeatureEnabled();
+#endif  // defined(ENABLE_SPELLCHECK) && defined(OS_ANDROID)
+
+}  // namespace spellcheck
+
+#endif  // COMPONENTS_SPELLCHECK_COMMON_SPELLCHECK_FEATURES_H_