Add UMA metrics and finch experiment for DTLS1.2 in WebRTC.

content/renderer/media/rtc_peer_connection_handler.cc

Index: content/renderer/media/rtc_peer_connection_handler.cc
diff --git a/content/renderer/media/rtc_peer_connection_handler.cc b/content/renderer/media/rtc_peer_connection_handler.cc
index 181838af564e9d0086921219e6c6eebed4a4e011..d2d741cb7acf538af9a1058126847f81c46514ac 100644
--- a/content/renderer/media/rtc_peer_connection_handler.cc
+++ b/content/renderer/media/rtc_peer_connection_handler.cc
@@ -14,6 +14,7 @@
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/metrics/histogram.h"
+#include "base/metrics/sparse_histogram.h"
 #include "base/stl_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/thread_task_runner_handle.h"
@@ -551,6 +552,41 @@ class PeerConnectionUMAObserver : public webrtc::UMAObserver {
     }
   }
 
+  void IncrementSparseEnumCounter(
+      webrtc::PeerConnectionEnumCounterType counter_type,
+      int counter) override {
+    switch (counter_type) {
+      case webrtc::kEnumCounterAudioSrtpCipher:
+        UMA_HISTOGRAM_SPARSE_SLOWLY(
+            "WebRTC.PeerConnection.SrtpCryptoSuite.Audio", counter);
+        break;
+      case webrtc::kEnumCounterAudioSslCipher:
+        UMA_HISTOGRAM_SPARSE_SLOWLY(
+            "WebRTC.PeerConnection.SslCipherSuite.Audio", counter);
+        break;
+      case webrtc::kEnumCounterVideoSrtpCipher:
+        UMA_HISTOGRAM_SPARSE_SLOWLY(
+            "WebRTC.PeerConnection.SrtpCryptoSuite.Video", counter);
+        break;
+      case webrtc::kEnumCounterVideoSslCipher:
+        UMA_HISTOGRAM_SPARSE_SLOWLY(
+            "WebRTC.PeerConnection.SslCipherSuite.Video", counter);
+        break;
+      case webrtc::kEnumCounterDataSrtpCipher:
+        UMA_HISTOGRAM_SPARSE_SLOWLY(
+            "WebRTC.PeerConnection.SrtpCryptoSuite.Data", counter);
+        break;
+      case webrtc::kEnumCounterDataSslCipher:
+        UMA_HISTOGRAM_SPARSE_SLOWLY(
+            "WebRTC.PeerConnection.SslCipherSuite.Data", counter);
+        break;
+      default:
+        // The default clause is expected to reach when new enum types are
+        // added.
+        break;
+    }
+  }
+
   void AddHistogramSample(webrtc::PeerConnectionUMAMetricsName type,
                           int value) override {
     // Runs on libjingle's signaling thread.