Allow MessageFilters to restrict listening to specific message classes

content/browser/histogram_message_filter.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_message_filter.h"
 
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/statistics_recorder.h"
 #include "content/browser/histogram_controller.h"
 #include "content/browser/tcmalloc_internals_request_job.h"
 #include "content/common/child_process_messages.h"
 #include "content/public/common/content_switches.h"
 
 namespace content {
 
-HistogramMessageFilter::HistogramMessageFilter() {}
+HistogramMessageFilter::HistogramMessageFilter()
+    : BrowserMessageFilter(ChildProcessMsgStart) {}
 
 bool HistogramMessageFilter::OnMessageReceived(const IPC::Message& message,
                                               bool* message_was_ok) {
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP_EX(HistogramMessageFilter, message, *message_was_ok)
     IPC_MESSAGE_HANDLER(ChildProcessHostMsg_ChildHistogramData,
                         OnChildHistogramData)
     IPC_MESSAGE_HANDLER(ChildProcessHostMsg_GetBrowserHistogram,
                         OnGetBrowserHistogram)
     IPC_MESSAGE_UNHANDLED(handled = false)
@@ skipping 27 matching lines @@
   base::HistogramBase* histogram =
       base::StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
     *histogram_json = "{}";
   } else {
     histogram->WriteJSON(histogram_json);
   }
 }
 
 }  // namespace content