Remove the unmaintained performance monitor.

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 7c724e0b618cf31af29c6ec375cba10537988c7c..30bd921d11d605e4a1361a104304383f16d05c80 100644
--- a/chrome/browser/performance_monitor/process_metrics_history.cc
+++ b/chrome/browser/performance_monitor/process_metrics_history.cc
@@ -8,7 +8,6 @@
 #include "base/metrics/histogram.h"
 #include "base/process/process_metrics.h"
 
-#include "chrome/browser/performance_monitor/constants.h"
 #include "chrome/browser/performance_monitor/process_metrics_history.h"
 #if defined(OS_MACOSX)
 #include "content/public/browser/browser_child_process_host.h"
@@ -17,6 +16,10 @@
 
 namespace performance_monitor {
 
+// If a process is consistently above this CPU utilization percentage over time,
+// we consider it as high and may take action.
+const float kHighCPUUtilizationThreshold = 90.0f;
+
 ProcessMetricsHistory::ProcessMetricsHistory()
     : process_handle_(0),
       process_type_(content::PROCESS_TYPE_UNKNOWN),