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

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 9a6492082af05bcf379ffede59e7d5f9f65ad7cd..94635f74a7f1f30722fddbb262fc973d1800f0a1 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -51741,6 +51741,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="WebRTC.PeerConnection.Cipher" enum="WebRTCSrtpCipherType">
+  <owner>guoweis@chromium.org</owner>
+  <summary>
+    Counters on the type of Ciphers used by WebRTC. This is collected when the
+    first transport signals the OnCompleted event.

[juberti2, 2015/09/24 13:29:43]

We might not have all the ciphers determined at the time the first transport
goes to completed, i.e. if we have multiple transports.

[guoweis_left_chromium, 2015/09/25 21:38:39]

I re-read the code. It has been changed recently and will trigger for each
transport.

+  </summary>
+</histogram>
+
 <histogram name="WebRTC.PeerConnection.ConnectionState"
     enum="IceConnectionStates">
   <owner>guoweis@chromium.org</owner>
@@ -74264,6 +74272,12 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="2" label="WEB_HISTORY_QUERY_TIMED_OUT">Timed out</int>
 </enum>
 
+<enum name="WebRTCSrtpCipherType" type="int">
+  <int value="0" label="Unknown"/>
+  <int value="1" label="AES_CM_128_HMAC_SHA1_32"/>
+  <int value="2" label="AES_CM_128_HMAC_SHA1_80"/>
+</enum>
+
 <enum name="WebsiteSettingsAction" type="int">
   <int value="0" label="Opened"/>
   <int value="1" label="Selected Permissions tab"/>
@@ -79330,6 +79344,21 @@ To add a new entry, add it with any value and run test to compute valid value.
   <affected-histogram name="WebFont.DecodeSpeed"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="WebRTCEncryptedChannelType" separator=".">
+  <suffix name="Srtp" label="SRTP"/>
+  <suffix name="Ssl" label="SSL"/>
+  <affected-histogram name="WebRTC.PeerConnection.Cipher.Audio"/>
+  <affected-histogram name="WebRTC.PeerConnection.Cipher.Data"/>
+  <affected-histogram name="WebRTC.PeerConnection.Cipher.Video"/>
+</histogram_suffixes>
+
+<histogram_suffixes name="WebRTCMediaType" separator=".">
+  <suffix name="Audio" label="Audio"/>
+  <suffix name="Video" label="Video"/>
+  <suffix name="Data" label="Data"/>
+  <affected-histogram name="WebRTC.PeerConnection.Cipher"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="WebStoreLinkExperiment">
   <suffix name="Disabled" label="Neither extra webstore link is visible"/>
   <suffix name="FooterLink" label="Link in bottom right of footer"/>