Update //third_party/protobuf to version 3.

third_party/protobuf/objectivec/DevTools/check_version_stamps.sh

+#!/bin/bash
+
+# This script checks that the runtime version number constant in the compiler
+# source and in the runtime source is the same.
+#
+# A distro can be made of the protobuf sources with only a subset of the
+# languages, so if the compiler depended on the Objective C runtime, those
+# builds would break. At the same time, we don't want the runtime source
+# depending on the compiler sources; so two copies of the constant are needed.
+
+set -eu
+
+readonly ScriptDir=$(dirname "$(echo $0 | sed -e "s,^\([^/]\),$(pwd)/\1,")")
+readonly ProtoRootDir="${ScriptDir}/../.."
+
+die() {
+    echo "Error: $1"
+    exit 1
+}
+
+readonly ConstantName=GOOGLE_PROTOBUF_OBJC_GEN_VERSION
+
+# Collect version from plugin sources.
+
+readonly PluginSrc="${ProtoRootDir}/src/google/protobuf/compiler/objectivec/objectivec_file.cc"
+readonly PluginVersion=$( \
+    cat "${PluginSrc}" \
+        | sed -n -e "s:const int32 ${ConstantName} = \([0-9]*\);:\1:p"
+)
+
+if [[ -z "${PluginVersion}" ]] ; then
+    die "Failed to find ${ConstantName} in the plugin source (${PluginSrc})."
+fi
+
+# Collect version from runtime sources.
+
+readonly RuntimeSrc="${ProtoRootDir}/objectivec/GPBBootstrap.h"
+readonly RuntimeVersion=$( \
+    cat "${RuntimeSrc}" \
+        | sed -n -e "s:#define ${ConstantName} \([0-9]*\):\1:p"
+)
+
+if [[ -z "${RuntimeVersion}" ]] ; then
+    die "Failed to find ${ConstantName} in the runtime source (${RuntimeSrc})."
+fi
+
+# Compare them.
+
+if [[ "${PluginVersion}" != "${RuntimeVersion}" ]] ; then
+    die "Versions don't match!
+   Plugin: ${PluginVersion} from ${PluginSrc}
+  Runtime: ${RuntimeVersion} from ${RuntimeSrc}
+"
+fi
+
+# Success