Support "shared" histograms between processes.

chrome/service/service_ipc_server.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 "chrome/service/service_ipc_server.h"
 
 #include "base/metrics/histogram_delta_serialization.h"
 #include "build/build_config.h"
 #include "chrome/common/service_messages.h"
 #include "ipc/ipc_logging.h"
@@ skipping 105 matching lines @@
 
   return handled;
 }
 
 void ServiceIPCServer::OnGetHistograms() {
   if (!histogram_delta_serializer_) {
     histogram_delta_serializer_.reset(
         new base::HistogramDeltaSerialization("ServiceProcess"));
   }
   std::vector<std::string> deltas;
-  histogram_delta_serializer_->PrepareAndSerializeDeltas(&deltas);
+  // "false" to SPerpareAndSerializeDeltas() indicates to *not* include

[Alexei Svitkine (slow), 2016/01/22 16:15:16]

Nit: SPerpareAndSerializeDeltas() -> PerpareAndSerializeDeltas()

[bcwhite, 2016/01/22 17:17:48]

Done.

+  // histograms held in persistent storage on the assumption that they will be
+  // visible to the recipient through other means.
+  histogram_delta_serializer_->PrepareAndSerializeDeltas(&deltas, false);
   channel_->Send(new ServiceHostMsg_Histograms(deltas));
 }
 
 void ServiceIPCServer::OnShutdown() {
   client_->OnShutdown();
 }
 
 void ServiceIPCServer::OnUpdateAvailable() {
   client_->OnUpdateAvailable();
 }