Add a switch to emit browser histograms.

base/metrics/statistics_recorder.cc

Index: base/metrics/statistics_recorder.cc
diff --git a/base/metrics/statistics_recorder.cc b/base/metrics/statistics_recorder.cc
index f23c81054cf5cff26915da0ae36ffd34f9e69050..e1de90474b1051be00c429370811ba631c0afbac 100644
--- a/base/metrics/statistics_recorder.cc
+++ b/base/metrics/statistics_recorder.cc
@@ -6,11 +6,13 @@
 
 #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;
@@ -163,6 +165,37 @@ void StatisticsRecorder::WriteGraph(const std::string& query,
 }
 
 // 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;