Don't fetch histograms from the same process.

content/browser/histogram_controller.cc

 // 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.
 
 #include "content/browser/histogram_controller.h"
 
 #include "base/bind.h"
 #include "base/metrics/histogram.h"
+#include "base/process/process_handle.h"
 #include "content/browser/histogram_subscriber.h"
 #include "content/common/child_process_messages.h"
 #include "content/public/browser/browser_child_process_host_iterator.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/child_process_data.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/common/process_type.h"
 
 namespace content {
 
@@ skipping 46 matching lines @@
   DCHECK_EQ(subscriber_, subscriber);
   subscriber_ = NULL;
 }
 
 void HistogramController::GetHistogramDataFromChildProcesses(
     int sequence_number) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
 
   int pending_processes = 0;
   for (BrowserChildProcessHostIterator iter; !iter.Done(); ++iter) {
-    int type = iter.GetData().process_type;
+    const ChildProcessData& data = iter.GetData();
+    int type = data.process_type;
     if (type != PROCESS_TYPE_PLUGIN &&
         type != PROCESS_TYPE_GPU &&
         type != PROCESS_TYPE_PPAPI_PLUGIN &&
         type != PROCESS_TYPE_PPAPI_BROKER) {
       continue;
     }
 
+    // In some cases, there may be no child process of the given type (for
+    // example, the GPU process may not exist and there may instead just be a
+    // GPU thread in the browser process). If that's the case, then the process
+    // handle will be base::kNullProcessHandle and we shouldn't ask it for data.
+    if (data.handle == base::kNullProcessHandle)
+      continue;
+
     ++pending_processes;
     if (!iter.Send(new ChildProcessMsg_GetChildHistogramData(sequence_number)))
       --pending_processes;
   }
 
   BrowserThread::PostTask(
       BrowserThread::UI,
       FROM_HERE,
       base::Bind(
           &HistogramController::OnPendingProcesses,
@@ skipping 19 matching lines @@
 
   BrowserThread::PostTask(
       BrowserThread::IO,
       FROM_HERE,
       base::Bind(&HistogramController::GetHistogramDataFromChildProcesses,
                  base::Unretained(this),
                  sequence_number));
 }
 
 }  // namespace content