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 c7a6b843898f0197b5982f07a03c6fc62acfc264..2c992de32f9fab25cbe504d77f0e60cf3e88d1ca 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -50390,6 +50390,22 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="WebRTC.PeerConnection.SrtpCrypto" enum="DTLS_SRTPCryptoSuite">

[Ryan Sleevi, 2015/09/27 02:37:46]

SrtpCryptoSuite?

[pthatcher2, 2015/09/29 21:59:43]

+1

+  <owner>guoweis@chromium.org</owner>
+  <summary>
+    Counters on the type of SRTP Cryptos used by WebRTC. This is collected

[Ryan Sleevi, 2015/09/27 02:37:46]

I'm not sure what "cryptos" is meant to convey, but it doesn't feel
grammatically correct.

Is this Crypto Suites? That seems to match your naming of the histogram. 

[pthatcher2, 2015/09/29 21:59:43]

+1 to crypto suites (no need to capitalize)

+    whenever the transport signals the OnCompleted event.
+  </summary>
+</histogram>
+
+<histogram name="WebRTC.PeerConnection.SslCipher" enum="SSLCipherSuite">

[Ryan Sleevi, 2015/09/27 02:37:46]

SslCipherSuite?

[pthatcher2, 2015/09/29 21:59:43]

+1

+  <owner>guoweis@chromium.org</owner>
+  <summary>
+    Counters on the type of SSL Ciphers used by WebRTC. This is collected

[Ryan Sleevi, 2015/09/27 02:37:46]

ciphersuites

+    whenever the transport signals the OnCompleted event.
+  </summary>
+</histogram>
+
 <histogram name="WebRTC.PeerConnection.TimeToConnect" units="milliseconds">
   <owner>mallinath@chromium.org</owner>
   <summary>Time to setup a peer to peer call with PeerConnection.</summary>
@@ -55046,6 +55062,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="2" label="Batch"/>
 </enum>
 
+<enum name="DTLS_SRTPCryptoSuite" type="int">
+  <summary>DTLS/SRTP crypto suites from the IANA registry</summary>

[Ryan Sleevi, 2015/09/27 02:37:46]

considering I've had to search for Justin's comments twice, since Google-foo
doesn't show the registry when searching for "SRTP crypto suite registry" (well,
it shows the SDP registrations but not the numeric forms Justin highlighted), it
may help to expand this comment to indicate the URL.

+  <int value="1" label="SRTP_AES128_CM_SHA1_80"/>
+  <int value="2" label="SRTP_AES128_CM_SHA1_32"/>
+  <int value="5" label="SRTP_NULL_SHA1_80"/>
+  <int value="6" label="SRTP_NULL_SHA1_32"/>
+</enum>
+
 <enum name="DumpOutcome" type="int">
   <int value="0" label="Success"/>
   <int value="1" label="Failure"/>
@@ -78625,6 +78649,14 @@ 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="WebRTCMediaType" separator=".">
+  <suffix name="Audio" label="Audio"/>
+  <suffix name="Video" label="Video"/>
+  <suffix name="Data" label="Data"/>
+  <affected-histogram name="WebRTC.PeerConnection.SrtpCrypto"/>
+  <affected-histogram name="WebRTC.PeerConnection.SslCipher"/>
+</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"/>