histogram synchronizer code between renderer and browser for UMA and about_histogram

chrome/renderer/renderer_histogram_snapshots.cc

 // Copyright (c) 2006-2008 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/renderer/renderer_histogram_snapshots.h"
 
 #include <ctype.h>
 
 #include "base/histogram.h"
 #include "base/logging.h"
 #include "base/message_loop.h"
 #include "base/pickle.h"
 #include "chrome/common/render_messages.h"
 #include "chrome/renderer/render_process.h"
 #include "chrome/renderer/render_thread.h"
 
 // TODO(raman): Before renderer shuts down send final snapshot lists.
 
 RendererHistogramSnapshots::RendererHistogramSnapshots()
     : ALLOW_THIS_IN_INITIALIZER_LIST(
         renderer_histogram_snapshots_factory_(this)) {
 }
 
 // Send data quickly!
-void RendererHistogramSnapshots::SendHistograms() {
+void RendererHistogramSnapshots::SendHistograms(int sequence_number) {
   RenderThread::current()->message_loop()->PostTask(FROM_HERE,
       renderer_histogram_snapshots_factory_.NewRunnableMethod(
-          &RendererHistogramSnapshots::UploadAllHistrograms));
+          &RendererHistogramSnapshots::UploadAllHistrograms, sequence_number));
 }
 
-void RendererHistogramSnapshots::UploadAllHistrograms() {
+void RendererHistogramSnapshots::UploadAllHistrograms(int sequence_number) {
   StatisticsRecorder::Histograms histograms;
   StatisticsRecorder::GetHistograms(&histograms);
 
   HistogramPickledList pickled_histograms;
 
   for (StatisticsRecorder::Histograms::iterator it = histograms.begin();
        histograms.end() != it;
        it++) {
     UploadHistrogram(**it, &pickled_histograms);
   }
-  // Send the handle over synchronous IPC.
-  if (pickled_histograms.size() > 0) {
-    RenderThread::current()->Send(
-        new ViewHostMsg_RendererHistograms(pickled_histograms));
-  }
+  // Send the sequence number and list of pickled histograms over synchronous
+  // IPC.
+  RenderThread::current()->Send(
+      new ViewHostMsg_RendererHistograms(
+          sequence_number, pickled_histograms));
 }
 
 // Extract snapshot data and then send it off the the Browser process
 // to save it.
 void RendererHistogramSnapshots::UploadHistrogram(
     const Histogram& histogram,
     HistogramPickledList* pickled_histograms) {
 
   // Get up-to-date snapshot of sample stats.
   Histogram::SampleSet snapshot;
@@ skipping 27 matching lines @@
     const Histogram::SampleSet& snapshot,
     HistogramPickledList* pickled_histograms) {
 
   DCHECK(0 != snapshot.TotalCount());
   snapshot.CheckSize(histogram);
 
   std::string histogram_info =
       Histogram::SerializeHistogramInfo(histogram, snapshot);
   pickled_histograms->push_back(histogram_info);
 }