PerformanceMonitor: Add a new UMA histograms to track average CPU utilization

chrome/browser/performance_monitor/process_metrics_history.cc

Index: chrome/browser/performance_monitor/process_metrics_history.cc
diff --git a/chrome/browser/performance_monitor/process_metrics_history.cc b/chrome/browser/performance_monitor/process_metrics_history.cc
index 9ac206fb36151817a4ccbe446fb28fab2d91d2f6..7bf658deda4821fcdeb4fd72e846bb9e3035ab70 100644
--- a/chrome/browser/performance_monitor/process_metrics_history.cc
+++ b/chrome/browser/performance_monitor/process_metrics_history.cc
@@ -74,9 +74,13 @@ void ProcessMetricsHistory::EndOfCycle() {
 
 void ProcessMetricsHistory::RunPerformanceTriggers() {
   // As an initial step, we only care about browser processes.
-  if (process_type_ != content::PROCESS_TYPE_BROWSER)
+  if (process_type_ != content::PROCESS_TYPE_BROWSER || sample_count_ == 0)
     return;
 
+  UMA_HISTOGRAM_CUSTOM_COUNTS("PerformanceMonitor.AverageCPU.BrowserProcess",
+                              accumulated_cpu_usage_ / sample_count_,
+                              0, 1200, 20);
+
   // If CPU usage has consistently been above our threshold,
   // we *may* have an issue.
   if (min_cpu_usage_ > kHighCPUUtilizationThreshold)