Avoid calling SetTaskRunner on RepeatingTimer.

This is to avoid a sequence checker debug error.

BUG=b/113298882
TEST=Manually tested on Linux workstation simulator.

Change-Id: I07b43e315335bf95e67b4567aedd4b7466cc5391
Reviewed-on: https://chromium-review.googlesource.com/1213950Reviewed-by: Nicholas Verne <nverne@chromium.org>
Commit-Queue: Tim Zheng <timzheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589715}

chrome/browser/chromeos/crostini/crosvm_metrics.cc

@@ -38,7 +38,6 @@ CrosvmMetrics::CrosvmMetrics()
            base::TaskShutdownBehavior::SKIP_ON_SHUTDOWN})),
       page_size_(sysconf(_SC_PAGESIZE)),
       weak_ptr_factory_(this) {
-  timer_.SetTaskRunner(task_runner_);
 }
 
 CrosvmMetrics::~CrosvmMetrics() = default;
@@ -95,6 +94,12 @@ int CrosvmMetrics::CalculateCrosvmCpuPercentage(
 }
 
 void CrosvmMetrics::MetricsCycleCallback() {
+  task_runner_->PostNonNestableTask(
+      FROM_HERE, base::BindOnce(&CrosvmMetrics::MetricsCycle,
+                                weak_ptr_factory_.GetWeakPtr()));
+}
+
+void CrosvmMetrics::MetricsCycle() {
   if (!cycle_start_data_collected_) {
     CollectCycleStartData();
     return;

chrome/browser/chromeos/crostini/crosvm_metrics.h

@@ -43,9 +43,12 @@ class CrosvmMetrics {
       int64_t cycle_cpu_time);
 
  private:
-  // Callback for resource metrics measurement and report.
+  // Callback to post MetricsCycle() to a blocking thread.
   void MetricsCycleCallback();
 
+  // Measures resource metrics and emit UMA histograms.
+  void MetricsCycle();
+
   // Collect the crosvm process data and system CPU usage data at the start of
   // the 10-minute cycle.
   void CollectCycleStartData();