Don't fetch histograms from the same process.

content/public/browser/child_process_data.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 CONTENT_PUBLIC_BROWSER_CHILD_PROCESS_DATA_H_
 #define CONTENT_PUBLIC_BROWSER_CHILD_PROCESS_DATA_H_
 
 #include "base/process/process.h"
 #include "base/strings/string16.h"
 #include "content/common/content_export.h"
 
 namespace content {
 
 // Holds information about a child process.
 struct ChildProcessData {
   // The type of the process.
   int process_type;
 
   // The name of the process.  i.e. for plugins it might be Flash, while for
   // for workers it might be the domain that it's from.
   base::string16 name;
 
   // The unique identifier for this child process. This identifier is NOT a
   // process ID, and will be unique for all types of child process for
   // one run of the browser.
   int id;
 
-  // The handle to the process.
+  // The handle to the process. May have value kNullProcessHandle if no process
+  // exists - either because it hasn't been started yet or it's running in the
+  // current process.
   base::ProcessHandle handle;
 
   explicit ChildProcessData(int process_type)
       : process_type(process_type), id(0), handle(base::kNullProcessHandle) {
   }
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_CHILD_PROCESS_DATA_H_