Refine systemInfo.cpu API defintions and provide systemInfo.cpu.get impl for Windows and Linux

chrome/browser/extensions/api/system_info_cpu/cpu_info_provider.h

 // Copyright (c) 2012 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.
 #ifndef CHROME_BROWSER_EXTENSIONS_API_SYSTEM_INFO_CPU_CPU_INFO_PROVIDER_H_
 #define CHROME_BROWSER_EXTENSIONS_API_SYSTEM_INFO_CPU_CPU_INFO_PROVIDER_H_
 
 #include "chrome/browser/extensions/system_info_provider.h"
+
+#include <vector>
+
 #include "chrome/common/extensions/api/experimental_system_info_cpu.h"
 
 namespace extensions {
 
 class CpuInfoProvider
     : public SystemInfoProvider<api::experimental_system_info_cpu::CpuInfo> {
  public:
+  typedef base::Callback<api::experimental_system_info_cpu::CpuUpdateInfo>
+      QueryCpuTimeCallback;
   virtual ~CpuInfoProvider() {}
 
+  // Overriden from SystemInfoProvider<CpuInfo>.
+  virtual bool QueryInfo(
+      api::experimental_system_info_cpu::CpuInfo* info) OVERRIDE;
+
+  // Start sampling the CPU usage. The callback gets called when one sampling
+  // cycle is completed periodically with the CPU updated usage info for each
+  // processors. Return true if it succeeds to start, otherwise, false is
+  // returned.
+  bool StartSampling(const QueryCpuTimeCallback& callback);
+
+  // Stop the sampling cycle. Return true if it succeeds to stop.
+  bool StopSampling();
+
   // Return the single shared instance of CpuInfoProvider.
   static CpuInfoProvider* Get();
+
+ private:
+  // The amount of time that CPU spent on performing different kinds of work.
+  // It is used to calculate the usage percent for processors.
+  struct CpuTime {
+    int64 user;   // user mode.
+    int64 kernel; // kernel mode.
+    int64 idle;   // twiddling thumbs.
+  };
+
+  // Platform specific implementation for querying the CPU time information
+  // for each processor. Note that the first element is the total aggregated
+  // numbers of all logic processors.
+  bool QueryCpuTimePerProcessor(std::vector<CpuTime>* times);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_SYSTEM_INFO_CPU_CPU_INFO_PROVIDER_H_