Roll webrtc to r2524.

DEPS

Index: DEPS
===================================================================
--- DEPS	(revision 147649)
+++ DEPS	(working copy)
@@ -62,7 +62,7 @@
   # the commit queue can handle CLs rolling Skia
   # and V8 without interference from each other.
   "v8_revision": "12118",
-  "webrtc_revision": "2486",
+  "webrtc_revision": "2524",
   "jsoncpp_revision": "248",
   "nss_revision": "145873",
 }