Update //third_party/protobuf to version 3.

third_party/protobuf/patches/0007-uninline_googleonce.patch

+unchanged:
+--- protobuf-cleaned/src/google/protobuf/stubs/once.cc  2015-12-30 13:21:46.000000000 -0800
++++ protobuf-patched/src/google/protobuf/stubs/once.cc  2016-03-31 13:25:32.180017848 -0700
+@@ -62,6 +62,13 @@
+ 
+ }  // namespace
+ 
++void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()) {
++  if (internal::Acquire_Load(once) != ONCE_STATE_DONE) {
++    internal::FunctionClosure0 func(init_func, false);
++    GoogleOnceInitImpl(once, &func);
++  }
++}
++
+ void GoogleOnceInitImpl(ProtobufOnceType* once, Closure* closure) {
+   internal::AtomicWord state = internal::Acquire_Load(once);
+   // Fast path. The provided closure was already executed.
+only in patch2:
+unchanged:
+--- protobuf-cleaned/src/google/protobuf/stubs/once.h   2015-12-30 13:21:46.000000000 -0800
++++ protobuf-patched/src/google/protobuf/stubs/once.h   2016-03-31 13:25:35.520013490 -0700
+@@ -122,12 +122,8 @@
+ LIBPROTOBUF_EXPORT
+ void GoogleOnceInitImpl(ProtobufOnceType* once, Closure* closure);
+ 
+-inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)()) {
+-  if (internal::Acquire_Load(once) != ONCE_STATE_DONE) {
+-    internal::FunctionClosure0 func(init_func, false);
+-    GoogleOnceInitImpl(once, &func);
+-  }
+-}
++LIBPROTOBUF_EXPORT
++void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)());
+ 
+ template <typename Arg>
+ inline void GoogleOnceInit(ProtobufOnceType* once, void (*init_func)(Arg*),