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

base/process/process_metrics.h

 // Copyright (c) 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.
 
 // This file contains routines for gathering resource statistics for processes
 // running on the system.
 
 #ifndef BASE_PROCESS_PROCESS_METRICS_H_
 #define BASE_PROCESS_PROCESS_METRICS_H_
 
@@ skipping 142 matching lines @@
   // Fills a WorkingSetKBytes containing resident private and shared memory
   // usage in bytes, as per definition of WorkingSetBytes.
   bool GetWorkingSetKBytes(WorkingSetKBytes* ws_usage) const;
 
   // Computes the current process available memory for allocation.
   // It does a linear scan of the address space querying each memory region
   // for its free (unallocated) status. It is useful for estimating the memory
   // load and fragmentation.
   bool CalculateFreeMemory(FreeMBytes* free) const;
 
-  // Returns the CPU usage in percent since the last time this method was
-  // called. The first time this method is called it returns 0 and will return
-  // the actual CPU info on subsequent calls.
-  // On Windows, the CPU usage value is for all CPUs. So if you have 2 CPUs and
-  // your process is using all the cycles of 1 CPU and not the other CPU, this
-  // method returns 50.
+  // Returns the CPU usage in percent since the last time this method or
+  // GetPlatformIndependentCPUUsage() was called. The first time this method
+  // is called it returns 0 and will return the actual CPU info on subsequent
+  // calls. On Windows, the CPU usage value is for all CPUs. So if you have
+  // 2 CPUs and your process is using all the cycles of 1 CPU and not the other
+  // CPU, this method returns 50.
   double GetCPUUsage();
 
+  // Same as GetCPUUsage(), but will return consistent values on all platforms
+  // (cancelling the Windows exception mentioned above) by returning a value in
+  // the range of 0 to (100 * numCPUCores) everywhere.
+  double GetPlatformIndependentCPUUsage();
+
   // Retrieves accounting information for all I/O operations performed by the
   // process.
   // If IO information is retrieved successfully, the function returns true
   // and fills in the IO_COUNTERS passed in. The function returns false
   // otherwise.
   bool GetIOCounters(IoCounters* io_counters) const;
 
  private:
 #if !defined(OS_MACOSX) || defined(OS_IOS)
   explicit ProcessMetrics(ProcessHandle process);
@@ skipping 175 matching lines @@
   SystemDiskInfo disk_info_;
 #endif
 #if defined(OS_CHROMEOS)
   SwapInfo swap_info_;
 #endif
 };
 
 }  // namespace base
 
 #endif  // BASE_PROCESS_PROCESS_METRICS_H_