Telemetry: adds CPU frequency stats.

tools/telemetry/telemetry/core/platform/platform_backend.py

Index: tools/telemetry/telemetry/core/platform/platform_backend.py
diff --git a/tools/telemetry/telemetry/core/platform/platform_backend.py b/tools/telemetry/telemetry/core/platform/platform_backend.py
index 695539d3087817de2ca93811e1e114b33210f2f0..5cc1f39d9fbe17715f0274b0310a970c4cf7f598 100644
--- a/tools/telemetry/telemetry/core/platform/platform_backend.py
+++ b/tools/telemetry/telemetry/core/platform/platform_backend.py
@@ -56,6 +56,9 @@ class PlatformBackend(object):
   def GetSystemTotalPhysicalMemory(self):
     raise NotImplementedError()
 
+  def GetGlobalCpuStats(self):

[tonyg, 2014/04/18 03:58:56]

We shouldn't need a new API method, right? Should GetCpuStats just include a
Global key?

Also, I'm wondering whether this should go into the StopMonitoringPower dict
instead. There's some other global power related stuff in there. I was thinking
c-states would go in there, so p-states probably make sense as well.

[bulach, 2014/04/22 12:43:10]

see above :)
hmm... tough choice: on one hand, this is certainly related to power stuff..
otoh, it feels a bit weird to have "%CPU per process" in the cpu metrics, and
then the frequency histogram separated out? happy to do it in
StopMonitoringPower, if you prefer, just explaining my reasoning..

+    return {}
+
   def GetCpuStats(self, pid):
     return {}