browser: Add Get{Vm,ArcSystem}ProcessList traces

While profiling Chrome on CrOS, we noticed a significant amount of time is
spent in Get{Vm,ArcSystem}ProcessList even if the task manager is not
running.

On a nocturne m3 we observed 2% total of the CPU used is spent in these
two functions.
This CL adds traces for those two functions.
Capturing a trace confirms that we call those two functions every few seconds
and they take about 80ms of CPU time each.

Bug: b/154362057
Change-Id: Ie851643dc1093e400282aeb976c880b9901f3138
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2153827Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Daniele Castagna <dcastagna@chromium.org>
Cr-Commit-Position: refs/heads/master@{#760949}

chrome/browser/chromeos/arc/process/arc_process_service.cc

@@ -68,8 +68,8 @@ base::ProcessId GetArcInitProcessId(
 }
 
 std::vector<ArcProcess> GetArcSystemProcessList() {
+  TRACE_EVENT0("browser", "GetArcSystemProcessList");
   std::vector<ArcProcess> ret_processes;
-
   if (arc::IsArcVmEnabled()) {
     // TODO(b/122992194): Fix this for ARCVM.
     return ret_processes;

chrome/browser/task_manager/providers/vm/vm_process_task_provider.cc

@@ -12,6 +12,7 @@
 #include "base/task/task_traits.h"
 #include "base/task/thread_pool.h"
 #include "base/threading/thread_task_runner_handle.h"
+#include "base/trace_event/trace_event.h"
 #include "chrome/browser/chromeos/crostini/crostini_util.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "chrome/browser/task_manager/providers/vm/crostini_process_task.h"
@@ -220,6 +221,7 @@ void VmProcessTaskProvider::StopUpdating() {
 }
 
 std::vector<VmProcessData> GetVmProcessList() {
+  TRACE_EVENT0("browser", "GetVmProcessList");
   std::vector<VmProcessData> ret_processes;
   const base::ProcessIterator::ProcessEntries& entry_list =
       base::ProcessIterator(nullptr).Snapshot();