[PowerProfiler] Power Profiler service should detect the sampling rate from the data provider.

content/browser/power_profiler/power_data_provider_ia_win.cc

Index: content/browser/power_profiler/power_data_provider_ia_win.cc
diff --git a/content/browser/power_profiler/power_data_provider_ia_win.cc b/content/browser/power_profiler/power_data_provider_ia_win.cc
index 597e3bd73ac53730372ab386ee9e3e6db6ede4c3..5a92aba23fb8089a5ccda572dfd3041cde5765cd 100644
--- a/content/browser/power_profiler/power_data_provider_ia_win.cc
+++ b/content/browser/power_profiler/power_data_provider_ia_win.cc
@@ -8,6 +8,11 @@
 
 namespace content {
 
+// Default sampling period, as recommended by Intel Power Gadget.
+// Section 3.1 of
+// http://software.intel.com/en-us/blogs/2013/10/03/using-the-intel-power-gadget-api-on-windows
+const int kDefaultSamplePeriodMs = 50;
+
 scoped_ptr<PowerDataProvider> PowerDataProvider::Create() {
   scoped_ptr<PowerDataProviderIA> provider(new PowerDataProviderIA());
   if (provider->Initialize())
@@ -54,6 +59,10 @@ PowerEventVector PowerDataProviderIA::GetData() {
   return events;
 }
 
+int64 PowerDataProviderIA::SamplingRate() {
+  return kDefaultSamplePeriodMs;
+}
+
 bool PowerDataProviderIA::Initialize() {
   if (is_open_)
     return true;