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

chrome/browser/performance_monitor/process_metrics_history.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <limits>
 
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/process/process_metrics.h"
 
@@ skipping 34 matching lines @@
 #if defined(OS_MACOSX)
   process_metrics_.reset(base::ProcessMetrics::CreateProcessMetrics(
       process_handle_, content::BrowserChildProcessHost::GetPortProvider()));
 #else
   process_metrics_.reset(
       base::ProcessMetrics::CreateProcessMetrics(process_handle_));
 #endif
 }
 
 void ProcessMetricsHistory::SampleMetrics() {
-  double cpu_usage = process_metrics_->GetCPUUsage();
+  double cpu_usage = process_metrics_->GetPlatformIndependentCPUUsage();
   min_cpu_usage_ = std::min(min_cpu_usage_, cpu_usage);
   accumulated_cpu_usage_ += cpu_usage;
 
   size_t private_bytes = 0;
   size_t shared_bytes = 0;
   if (!process_metrics_->GetMemoryBytes(&private_bytes, &shared_bytes))
     LOG(WARNING) << "GetMemoryBytes returned NULL (platform-specific error)";
 
   accumulated_private_bytes_ += private_bytes;
   accumulated_shared_bytes_ += shared_bytes;
 
   sample_count_++;
 }
 
 void ProcessMetricsHistory::EndOfCycle() {
   RunPerformanceTriggers();
   ResetCounters();
 }
 
 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;
 
+  // We scale up to the equivalent of 64 CPU cores fully loaded. More than this
+  // doesn't really matter, as we're already in a terrible place.
+  UMA_HISTOGRAM_CUSTOM_COUNTS("PerformanceMonitor.AverageCPU.BrowserProcess",
+                              accumulated_cpu_usage_ / sample_count_,
+                              0, 6400, 50);
+
   // If CPU usage has consistently been above our threshold,
   // we *may* have an issue.
   if (min_cpu_usage_ > kHighCPUUtilizationThreshold)
     UMA_HISTOGRAM_BOOLEAN("PerformanceMonitor.HighCPU.BrowserProcess", true);
 }
 
 }  // namespace performance_monitor