add /img/n/m endpoint to skiaserve

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1755563003

Review URL: https://codereview.chromium.org/1755563003
diff --git a/include/private/GrAuditTrail.h b/include/private/GrAuditTrail.h
index f9b0091..4d2d99a 100644
--- a/include/private/GrAuditTrail.h
+++ b/include/private/GrAuditTrail.h
@@ -119,6 +119,7 @@
     };
 
     void getBoundsByClientID(SkTArray<BatchInfo>* outInfo, int clientID);
+    void getBoundsByBatchListID(BatchInfo* outInfo, int batchListID);
 
     void fullReset();
 
@@ -147,6 +148,8 @@
     };
     typedef SkTArray<SkAutoTDelete<BatchNode>, true> BatchList;
 
+    void copyOutFromBatchList(BatchInfo* outBatchInfo, int batchListID);
+
     template <typename T>
     static void JsonifyTArray(SkString* json, const char* name, const T& array,
                               bool addComma);