Add new reporting queue priority - manual upload only.

Bug: b:161266545
Change-Id: Ia50275969032a706299a77ef1d6cd8482fbd83cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2298221Reviewed-by: Sergey Poromov <poromov@chromium.org>
Reviewed-by: Zach Trudo <zatrudo@google.com>
Commit-Queue: Leonid Baraz <lbaraz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#788662}

components/policy/proto/record_constants.proto

@@ -46,9 +46,19 @@ enum Priority {
   SLOW_BATCH = 3;
 
   // |BACKGROUND_BATCH| queues transfer large amounts of non-immediate data.
-  // These records are the first to be rate limited.
-  // |BACKGROUND_BATCH| records are the first to be shed.
+  // These records will be rate limited before |SLOW_BATCH| records.
+  // |BACKGROUND_BATCH| records are shed before |SLOW_BATCH| records.
   // Log files are a perfect examples of records that need to be
   // |BACKGROUND_BATCH|.
   BACKGROUND_BATCH = 4;
+
+  // |MANUAL_BATCH| queues transfer data only on explicit request.
+  // Note that since a queue can hold records submitted by multiple clients,
+  // one client requesting to transfer data will do so for all collected
+  // records of the same priority, including those enqueued by other clients.
+  // |MANUAL_BATCH| records are the first to be rate limited, and since there
+  // is no automatic transfer, it is important to explicitly flush them often
+  // enough to avoid loss of data.
+  // |MANUAL_BATCH| records are the first to be shed.
+  MANUAL_BATCH = 5;
 }