Update execution_context.proto from Google3

Bug: internal bug id b/130928904
Change-Id: I051aa85d6e43e92b66b37ec420fbcc70060ac79b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1814674
Commit-Queue: Bin Du <dubin@google.com>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699428}

third_party/metrics_proto/README.chromium

 Name: Metrics Protos
 Short Name: metrics_proto
 URL: This is the canonical public repository
-Version: 270770521
-Date: 2019/09/23 UTC
+Version: 270927279
+Date: 2019/09/24 UTC
 License: BSD
 Security Critical: Yes
 

third_party/metrics_proto/execution_context.proto

@@ -61,6 +61,12 @@ enum Thread {
 
   SERVICE_WORKER_THREAD = 15;
 
+  // Thread pool thread (in renderer process).
+  THREAD_POOL_THREAD = 16;
+
+  // GPU memory thread (in renderer process).
+  GPU_MEMORY_THREAD = 17;
+
   // A Chrome thread not identified by any other enum. Defined for the benefit
   // of Chrome OS. Do not use for the Chrome sampling profiler; define a new
   // enum instead.