Land https://codereview.chromium.org/889083003/ to update libsrtp to upstream 1.5.0

srtp/CHANGES

Index: srtp/CHANGES
===================================================================
--- srtp/CHANGES	(revision 294174)
+++ srtp/CHANGES	(working copy)
@@ -1,5 +1,49 @@
 Changelog
 
+1.5.1
+
+  Pull request 95 - Additional header check from Chromium
+
+  Pull request 94 - Add missing copyright headers. 
+
+  Pull request 90 - Fix out-of-source tree builds.
+
+  Pull request 89 - Introduce little endian RISC support
+
+  Pull request 86 - Add support for cross-compiling the shared library for Windows and OS X
+
+  Pull request 85 - Add -f <pcap filter> option to rtp_decoder
+
+  Pull request 84 - Avoid problems due to unsafe macros
+
+  Pull request 82 - Align the AES ICM nonce
+
+  Pull request 80 - Take advantage of base64 conversion in testapps
+
+  Pull request 75 - Cleanup: miscellaneous cleanup of initial OpenSSL AES support
+
+  Pull request 74 - Allow testing with pcap file or capture - Issue #45
+
+  Other trivial fixes are included as well.  Please see github for details.
+
+1.5.0
+ 
+  Add support for using OpenSSL crypto using the --enable-openssl 
+  option.
+
+  Add support for AES-GCM crypto suites. 
+
+  Add support for pkg_config.
+
+  Add user data API to allow user to associate additional data with a 
+  SRTP context.
+
+  This release also includes a variety of bug fixes, which can be 
+  viewed at: https://github.com/cisco/libsrtp/commits/master
+
+  Note: The change log was not maintained between versions 1.3.20 and
+        1.4.5.
+
 1.3.20
 
   Lots of changes.  Thanks to Jeff Chan for catching a memory leak and