NaCl: Update revision in DEPS, r6880 -> r6904

This pulls in the following Native Client changes:

r6881: (ncbray) Re-enable PyAuto and fix a regression that crept in.
r6882: (sehr) Re-enable read sandboxing for ARM.  Not yet validating that it is required.
r6883: (pdox) Fix the signature of pthread_cond_timedwait. The timespec argument is const.
r6884: (krasin) Run at least some of TLS tests with newlib.
r6885: (eugenis) Disable debug_stub_test under ASan.
r6886: (halyavin) Test that we accept rex prefixes with bits which are not used by the command.
r6887: (dschuff) Remove ignore-validator flag from gcc spec run script
r6888: (noelallen) Add GYP building of untrusted code to NaCl
r6889: (sehr) Add validator support for checking that reads are sandboxed.  This cannot be
r6890: (sehr) Revert change 6889.  Clang transition is not complete, and will break things
r6891: (bsy) remove scaffolding needed for dual-repo changes.
r6892: (ncbray) Revert 6891, which broke the Mac Clang bot.
r6893: (pdox) Update UPSTREAM_REV and LLVM_PROJECT_REV to activate
r6894: (pdox) * Pull libgcc_s.so and libstdc++.so from native GLibC toolchain into PNaCl.
r6895: (eugenis) Code style tweak.
r6896: (krasin) Add run_irt_present_test_irt to test that irt is present.
r6897: (bradnelson) Gyp's expansion rules are iffy.
r6898: (mcgrathr) Update binutils to 73acd6f
r6899: (pdox) Roll toolchain DEPS to 6896.
r6900: (jasonwkim) Fix unused var warning/error
r6901: (dschuff) Utman fix for building JIT
r6902: (noelallen) Update untrusted GYP build to support 32bit.
r6903: (jvoung) Point pnacl glibc NACL_SDK_INCLUDE somewhere that exists.
r6904: (nfullagar) Add option to compile out NaClLog.

BUG=none
TEST=nacl_integration


Review URL: http://codereview.chromium.org/8228022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@105007 0039d316-1c4b-4281-b951-d872f2087c98

DEPS

@@ -7,7 +7,7 @@ vars = {
   "webkit_revision": "97166",
   "chromium_git": "http://git.chromium.org/git",
   "swig_revision": "69281",
-  "nacl_revision": "6880",
+  "nacl_revision": "6904",
   # After changing nacl_revision, run 'glient sync' and check native_client/DEPS
   # to update other nacl_*_revision's.
   # TODO(brettw) We should use the "From" syntax to avoid hardcoding the