[tracing] Dump child processes' memory metrics in browser

base/process/process_metrics_linux.cc

Index: base/process/process_metrics_linux.cc
diff --git a/base/process/process_metrics_linux.cc b/base/process/process_metrics_linux.cc
index bcebcf5729fda730528c49119c3c58c19e0ac6dc..7a731bb7851547979967ee7e68f044e8caa3960a 100644
--- a/base/process/process_metrics_linux.cc
+++ b/base/process/process_metrics_linux.cc
@@ -86,7 +86,8 @@ size_t ReadProcStatusAndGetFieldAsSizeT(pid_t pid, const std::string& field) {
       return value;
     }
   }
-  NOTREACHED();
+  // This can be reached if the process dies when proc is read -- in that case,
+  // the kernel can return missing fields.
   return 0;
 }