Fix regression in Linux/Android CPU measurement

A copy-paste error in https://crrev.com/c/5354013 resulted in CPU
measurements on Linux and Android adding user CPU twice, and ignoring
system CPU, instead of summing user and system CPU.

Bug: 332913220
Change-Id: Iee6d13623eda5cb3e3dd805f437e7be9da41f8ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5425458
Auto-Submit: Joe Mason <joenotcharles@google.com>
Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1282666}
diff --git a/base/process/process_metrics_linux.cc b/base/process/process_metrics_linux.cc
index 5a0989e9..7bc2350 100644
--- a/base/process/process_metrics_linux.cc
+++ b/base/process/process_metrics_linux.cc
@@ -73,7 +73,7 @@
   }
   const std::optional<int64_t> stime =
       internal::GetProcStatsFieldAsOptionalInt64(proc_stats,
-                                                 internal::VM_UTIME);
+                                                 internal::VM_STIME);
   if (stime.value_or(-1) < 0) {
     return base::unexpected(ProcessCPUUsageError::kSystemError);
   }