Roll webrtc to 2538.

DEPS

 # When adding a new dependency, please update the top-level .gitignore file
 # to list the dependency's destination directory.
 
 vars = {
   # Use this googlecode_url variable only if there is an internal mirror for it.
   # If you do not know, use the full path while defining your new deps entry.
   "googlecode_url": "http://%s.googlecode.com/svn",
   "sourceforge_url": "http://%(repo)s.svn.sourceforge.net/svnroot/%(repo)s",
   "webkit_trunk": "http://svn.webkit.org/repository/webkit/trunk",
   "nacl_trunk": "http://src.chromium.org/native_client/trunk",
@@ skipping 44 matching lines @@
   # checkouts and the other for Git checkouts.
   "ffmpeg_revision": "148611",
   "ffmpeg_hash": "4287c0271f399b98eb6851e6e650098f26b8c3c2",
 
   "sfntly_revision": "134",
   "skia_revision": "4834",
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling Skia
   # and V8 without interference from each other.
   "v8_revision": "12227",
-  "webrtc_revision": "2529",
+  "webrtc_revision": "2538",
   "jsoncpp_revision": "248",
   "nss_revision": "145873",
 }
 
 deps = {
   "src/breakpad/src":
     (Var("googlecode_url") % "google-breakpad") + "/trunk/src@999",
 
   "src/googleurl":
     (Var("googlecode_url") % "google-url") + "/trunk@175",
@@ skipping 492 matching lines @@
     "pattern": ".",
     "action": ["python", "src/build/util/lastchange.py",
                "-o", "src/build/util/LASTCHANGE"],
   },
   {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     "pattern": ".",
     "action": ["python", "src/build/gyp_chromium"],
   },
 ]