Implement server-suggested update check backoff

chrome/browser/android/webapk/webapk.proto

Index: chrome/browser/android/webapk/webapk.proto
diff --git a/chrome/browser/android/webapk/webapk.proto b/chrome/browser/android/webapk/webapk.proto
index 27fc96b0842a89ebad031e709b97ba27c5b6126d..6ff9e126638d99c051684136375e9ba335d79204 100644
--- a/chrome/browser/android/webapk/webapk.proto
+++ b/chrome/browser/android/webapk/webapk.proto
@@ -26,7 +26,14 @@ message WebApkResponse {
   // Unique id identifying session with WebAPK server.
   optional string token = 6;
 
-  reserved 4, 5;
+  // If true, this directs the client to check for updates less frequently than
+  // normal. This flag may be used, for example, if the WAM server knows that
+  // the client has an up-to-date WebAPK, but the client is unable to determine
+  // that for itself. Therefore, we want the client to back off from spamming
+  // update requests too often.
+  optional bool infrequent_updates = 8;
+
+  reserved 4, 5, 7;
 }
 
 // Sent as part of request to create or update a WebAPK.