Update //third_party/protobuf to version 3.

third_party/protobuf/python/tox.ini

Index: third_party/protobuf/python/tox.ini
diff --git a/third_party/protobuf/python/tox.ini b/third_party/protobuf/python/tox.ini
new file mode 100644
index 0000000000000000000000000000000000000000..301335bd41e9a3697d6a3d2185f0d956c66ad149
--- /dev/null
+++ b/third_party/protobuf/python/tox.ini
@@ -0,0 +1,26 @@
+[tox]
+envlist =
+    py{26,27,33,34}-{cpp,python}
+
+[testenv]
+usedevelop=true
+passenv = CC
+setenv =
+    cpp: LD_LIBRARY_PATH={toxinidir}/../src/.libs
+    cpp: DYLD_LIBRARY_PATH={toxinidir}/../src/.libs
+    cpp: PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION=cpp
+commands =
+    python setup.py -q build_py
+    python: python setup.py -q build
+    cpp: python setup.py -q build --cpp_implementation --warnings_as_errors
+    python: python setup.py -q test -q
+    cpp: python setup.py -q test -q --cpp_implementation
+# TODO(xiaofeng): Disabled because the Python testee program crashes on
+# some conformance test inputs.
+# python: python setup.py -q test_conformance
+# cpp: python setup.py -q test_conformance --cpp_implementation
+deps =
+    # Keep this list of dependencies in sync with setup.py.
+    six>=1.9
+    py26: ordereddict
+    py26: unittest2