[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 81463321cdb5fdb7245ccfce945b70eddbc6e35c..4b1fd64f8e9f52b59015e48715cc3e588eeb3f27 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/sync/driver/sync_driver_switches.h"
@@ -856,7 +857,7 @@ 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,