Collect histograms from Plugins and GPU processes child processes only

content/browser/histogram_controller.h

Index: content/browser/histogram_controller.h
===================================================================
--- content/browser/histogram_controller.h	(revision 152367)
+++ content/browser/histogram_controller.h	(working copy)
@@ -57,7 +57,9 @@
  private:
   friend struct DefaultSingletonTraits<HistogramController>;
 
-  // Contact child processes and get their histogram data.
+  // Contact PLUGIN and GPU child processes and get their histogram data.
+  // TODO(rtenneti): Enable getting histogram data for other processes like
+  // PPAPI and NACL.
   void GetHistogramDataFromChildProcesses(int sequence_number);
 
   HistogramSubscriber* subscriber_;