Add new QuicErrorCode to histograms.xml.

Review URL: https://chromiumcodereview.appspot.com/23454015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221956 0039d316-1c4b-4281-b951-d872f2087c98

tools/metrics/histograms/histograms.xml

@@ -23896,6 +23896,9 @@ other types of suffix sets.
   <int value="46" label="INVALID_STREAM_DATA"/>
   <int value="47" label="INVALID_CONGESTION_FEEDBACK_DATA"/>
   <int value="48" label="MISSING_PAYLOAD"/>
+  <int value="49" label="INVALID_PRIORITY"/>
+  <int value="50" label="INVALID_STREAM_FRAME"/>
+  <int value="51" label="PACKET_READ_ERROR"/>
 </enum>
 
 <enum name="QuicHandshakeState" type="int">