Merge third_party/libsrtp from https://chromium.googlesource.com/chromium/deps/libsrtp.git at dcc1fc62771b4f25fa5f91cddec8e9a491d0ee6d

This commit was generated by merge_from_chromium.py.

Change-Id: I49348face45e38650cfe7adb528cd1fa5e24b2eb