Add a switch to emit browser histograms.

base/metrics/statistics_recorder.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 "base/metrics/statistics_recorder.h"
 
 #include "base/at_exit.h"
 #include "base/debug/leak_annotations.h"
+#include "base/json/string_escape.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/stringprintf.h"
 #include "base/synchronization/lock.h"
+#include "base/values.h"
 
 using std::list;
 using std::string;
 
 namespace {
 // Initialize histogram statistics gathering system.
 base::LazyInstance<base::StatisticsRecorder>::Leaky g_statistics_recorder_ =
     LAZY_INSTANCE_INITIALIZER;
 }  // namespace
 
@@ skipping 132 matching lines @@
   GetSnapshot(query, &snapshot);
   for (Histograms::iterator it = snapshot.begin();
        it != snapshot.end();
        ++it) {
     (*it)->WriteAscii(output);
     output->append("\n");
   }
 }
 
 // static
+std::string StatisticsRecorder::ToJSON(const std::string& query) {
+  if (!IsActive())
+    return std::string();
+
+  std::string output("{");
+  if (query.length()) {

[Peter Kasting, 2013/11/14 07:04:06]

Nit: Use !empty()

[grt (UTC plus 2), 2013/11/14 14:44:12]

Done.

+    output.append("\"query\":");

[Peter Kasting, 2013/11/14 07:04:06]

Nit: All these append() calls could just be +=

[grt (UTC plus 2), 2013/11/14 14:44:12]

Done.

+    JsonDoubleQuote(query, true, &output);
+    output.append(",");
+  }
+
+  Histograms snapshot;
+  GetSnapshot(query, &snapshot);
+  output.append("\"histograms\":[");
+  std::string json;
+  bool first_time = true;

[Peter Kasting, 2013/11/14 07:04:06]

Nit: |first_histogram|?

[grt (UTC plus 2), 2013/11/14 14:44:12]

Done.

+  for (Histograms::const_iterator it = snapshot.begin(); it != snapshot.end();
+       ++it) {
+    if (first_time)
+      first_time = false;
+    else
+      output.append(",");
+    json.clear();

[Peter Kasting, 2013/11/14 07:04:06]

Nit: Instead of trying to micro-optimize with clear(), we should just declare
|json| here.

[grt (UTC plus 2), 2013/11/14 14:44:12]

Leaving this as-is.

[Peter Kasting, 2013/11/14 21:26:16]

OK... is there a big advantage to doing things this way?  This extends the
apparent lifetime of the temp, which is not only more confusing to read, it
hurts compiler attempts to optimize away the underlying variable.

[grt (UTC plus 2), 2013/11/14 21:52:27]

I believe that reuse of the underlying buffer will reduce the number of heap
operations. Is the compiler smart enough to know the underlying implementation
of std::string and know that it doesn't need to call its dtor/ctor on each
iteration?

+    (*it)->WriteJSON(&json);
+    output.append(json);
+  }
+  output.append("]}");
+  return output;
+}
+
+// static
 void StatisticsRecorder::GetHistograms(Histograms* output) {
   if (lock_ == NULL)
     return;
   base::AutoLock auto_lock(*lock_);
   if (histograms_ == NULL)
     return;
 
   for (HistogramMap::iterator it = histograms_->begin();
        histograms_->end() != it;
        ++it) {
@@ skipping 107 matching lines @@
 
 
 // static
 StatisticsRecorder::HistogramMap* StatisticsRecorder::histograms_ = NULL;
 // static
 StatisticsRecorder::RangesMap* StatisticsRecorder::ranges_ = NULL;
 // static
 base::Lock* StatisticsRecorder::lock_ = NULL;
 
 }  // namespace base