Add AppServiceInstanceRegistry flag.

kAppServiceInstanceRegistry is used to checked whether AppService
Instance Registry feature is used. The default value is set as disable.
When AppService Instance Registry feature is done,the flag will be
marked as enable.

BUG=1011235

Change-Id: If1fadd8cf1079c59141980c282b8506919252a6a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1890511
Commit-Queue: Nancy Wang <[email protected]>
Reviewed-by: Dominick Ng <[email protected]>
Cr-Commit-Position: refs/heads/master@{#711137}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 053e7ef..8cedbe1 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1861,6 +1861,9 @@
 extern const char kAppServiceAshName[];
 extern const char kAppServiceAshDescription[];
 
+extern const char kAppServiceInstanceRegistryName[];
+extern const char kAppServiceInstanceRegistryDescription[];
+
 extern const char kAppServiceIntentHandlingName[];
 extern const char kAppServiceIntentHandlingDescription[];