Add EXTERNAL_FILE option for ninja weight list

Test: m --ninja_weight_source=file,<file path>
Bug: 271527305
Change-Id: Ibeae4c757dff281be69486a9758dbee3584d9dec
diff --git a/ui/metrics/metrics_proto/metrics.proto b/ui/metrics/metrics_proto/metrics.proto
index 5e9a055..7e5516d 100644
--- a/ui/metrics/metrics_proto/metrics.proto
+++ b/ui/metrics/metrics_proto/metrics.proto
@@ -138,6 +138,7 @@
     NOT_USED = 0;
     NINJA_LOG = 1;
     EVENLY_DISTRIBUTED = 2;
+    EXTERNAL_FILE = 3;
   }
 
   optional bool use_goma = 1;
@@ -163,6 +164,7 @@
   // NOT_USED - ninja doesn't use weight list.
   // NINJA_LOG - ninja uses weight list based on previous builds by ninja log
   // EVENLY_DISTRIBUTED - ninja thinks every task has the same weight.
+  // EXTERNAL_FILE - ninja uses an external custom weight list
   optional NinjaWeightListSource ninja_weight_list_source = 8 [default = NOT_USED];
 }