[Android] Add flags for Clank language decouple

This CL adds just the feature flag for the Clank language decouple.  Three
more CLs will add the rest of the feature.

The feature flag DETAILED_LANGUAGE_SETTINGS is added to be used for both
the initial language decuple and new Android language settings.

Bug: 1068667
Change-Id: I9e999f44e6f431bb1f13d16f170d626f8819db45
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2360591Reviewed-by: David Vallet <dvallet@chromium.org>
Reviewed-by: Megan Jablonski <megjablon@chromium.org>
Commit-Queue: Trevor  Perrier <perrier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#802438}

chrome/browser/flags/android/chrome_feature_list.cc

@@ -231,6 +231,7 @@ const base::Feature* kFeaturesExposedToJava[] = {
     &net::features::kCookiesWithoutSameSiteMustBeSecure,
     &paint_preview::kPaintPreviewDemo,
     &paint_preview::kPaintPreviewShowOnStartup,
+    &language::kDetailedLanguageSettings,
     &language::kExplicitLanguageAsk,
     &ntp_snippets::kArticleSuggestionsFeature,
     &offline_pages::kOfflineIndicatorFeature,

chrome/browser/flags/android/java/src/org/chromium/chrome/browser/flags/ChromeFeatureList.java

@@ -280,6 +280,7 @@ public abstract class ChromeFeatureList {
             "DarkenWebsitesCheckboxInThemesSetting";
     public static final String DECOUPLE_SYNC_FROM_ANDROID_MASTER_SYNC =
             "DecoupleSyncFromAndroidMasterSync";
+    public static final String DETAILED_LANGUAGE_SETTINGS = "DetailedLanguageSettings";
     public static final String DIRECT_ACTIONS = "DirectActions";
     public static final String DNS_OVER_HTTPS = "DnsOverHttps";
     public static final String DOWNLOAD_FILE_PROVIDER = "DownloadFileProvider";

components/language/core/common/language_experiments.cc

@@ -30,6 +30,8 @@ const base::Feature kUseFluentLanguageModel {
 };
 const base::Feature kNotifySyncOnLanguageDetermined{
     "NotifySyncOnLanguageDetermined", base::FEATURE_ENABLED_BY_DEFAULT};
+const base::Feature kDetailedLanguageSettings{
+    "DetailedLanguageSettings", base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Params:
 const char kBackoffThresholdKey[] = "backoff_threshold";

components/language/core/common/language_experiments.h

@@ -36,6 +36,9 @@ extern const base::Feature kNotifySyncOnLanguageDetermined;
 // This feature uses the existing UI for translate bubble.
 extern const base::Feature kUseButtonTranslateBubbleUi;
 
+// This feature enables setting the application language on Android.
+extern const base::Feature kDetailedLanguageSettings;
+
 enum class OverrideLanguageModel {
   DEFAULT,
   FLUENT,