Reland: Enable AppService InstanceRegistry feature.

BUG=1011235

Change-Id: I2bb653c806bb6d749158dfcec5bfee78ac613f42
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1984793
Commit-Queue: Nancy Wang <nancylingwang@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727938}

chrome/common/chrome_features.cc

@@ -64,7 +64,7 @@ const base::Feature kAppNotificationStatusMessaging{
 #if !defined(OS_ANDROID)
 // App Service related flags. See chrome/services/app_service/README.md.
 const base::Feature kAppServiceInstanceRegistry{
-    "AppServiceInstanceRegistry", base::FEATURE_DISABLED_BY_DEFAULT};
+    "AppServiceInstanceRegistry", base::FEATURE_ENABLED_BY_DEFAULT};
 const base::Feature kAppServiceIntentHandling{
     "AppServiceIntentHandling", base::FEATURE_DISABLED_BY_DEFAULT};
 const base::Feature kAppServiceShelf{"AppServiceShelf",