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

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index bdd12c64d47f30cfee2c71f1bf86c462cb9f925d..366fa7f7c0dd479999e4016733f47ad3b70c082c 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -54,6 +54,7 @@
 #include "components/search/search_switches.h"
 #include "components/security_state/switches.h"
 #include "components/signin/core/common/signin_switches.h"
+#include "components/spellcheck/common/spellcheck_features.h"
 #include "components/spellcheck/common/spellcheck_switches.h"
 #include "components/ssl_config/ssl_config_switches.h"
 #include "components/strings/grit/components_strings.h"
@@ -835,7 +836,7 @@ const FeatureEntry kFeatureEntries[] = {
 #if defined(ENABLE_SPELLCHECK) && defined(OS_ANDROID)
     {"enable-android-spellchecker", IDS_OPTIONS_ENABLE_SPELLCHECK,
      IDS_OPTIONS_ENABLE_ANDROID_SPELLCHECKER_DESCRIPTION, kOsAndroid,
-     SINGLE_VALUE_TYPE(spellcheck::switches::kEnableAndroidSpellChecker)},
+     FEATURE_VALUE_TYPE(spellcheck::kAndroidSpellChecker)},
 #endif
     {"enable-scroll-prediction", IDS_FLAGS_SCROLL_PREDICTION_NAME,
      IDS_FLAGS_SCROLL_PREDICTION_DESCRIPTION, kOsDesktop,