NaCl: Update revision in DEPS, r13611 -> r13613

This pulls in the following Native Client changes:

r13612: (mseaborn) Disable the imc_mem_obj_create() syscall by default
r13613: (dschuff) Update revision for PNaCl r13557->r13609

BUG=none
TEST=browser_tests and nacl_integration
CQ_EXTRA_TRYBOTS=tryserver.chromium.linux:linux_rel_precise32,linux_nacl_sdk_build

Review URL: https://codereview.chromium.org/472893002

Cr-Commit-Position: refs/heads/master@{#289675}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289675 0039d316-1c4b-4281-b951-d872f2087c98

DEPS

@@ -35,7 +35,7 @@ vars = {
   "skia_git": "https://skia.googlesource.com",
   "boringssl_git": "https://boringssl.googlesource.com",
   "swig_revision": "230490",
-  "nacl_revision": "13611",
+  "nacl_revision": "13613",
   # After changing nacl_revision, run 'glient sync' and check native_client/DEPS
   # to update other nacl_*_revision's.
   "nacl_tools_revision": "13077",  # native_client/DEPS: tools_rev