Upgrade V8 to 5.1.281.57  DO NOT MERGE

FPIIM-449

Change-Id: Id981b686b4d587ac31697662eb98bb34be42ad90
(cherry picked from commit 3b9bc31999c9787eb726ecdbfd5796bfdec32a18)
diff --git a/infra/config/cq.cfg b/infra/config/cq.cfg
index fbf090b..5f85111 100644
--- a/infra/config/cq.cfg
+++ b/infra/config/cq.cfg
@@ -65,13 +65,14 @@
         name: "v8_win_rel_ng_triggered"
         triggered_by: "v8_win_rel_ng"
       }
-    }
-    buckets {
-      name: "tryserver.v8"
       builders {
         name: "v8_linux_blink_rel"
         experiment_percentage: 20
       }
+      builders {
+        name: "v8_linux64_sanitizer_coverage_rel"
+        experiment_percentage: 100
+      }
     }
   }