Update //third_party/protobuf to version 3.

third_party/protobuf/objectivec/Tests/text_format_map_unittest_data.txt

+map_int32_int32 {
+  key: 100
+  value: 1
+}
+map_int64_int64 {
+  key: 101
+  value: 1
+}
+map_uint32_uint32 {
+  key: 102
+  value: 1
+}
+map_uint64_uint64 {
+  key: 103
+  value: 1
+}
+map_sint32_sint32 {
+  key: 104
+  value: 1
+}
+map_sint64_sint64 {
+  key: 105
+  value: 1
+}
+map_fixed32_fixed32 {
+  key: 106
+  value: 1
+}
+map_fixed64_fixed64 {
+  key: 107
+  value: 1
+}
+map_sfixed32_sfixed32 {
+  key: 108
+  value: 1
+}
+map_sfixed64_sfixed64 {
+  key: 109
+  value: 1
+}
+map_int32_float {
+  key: 110
+  value: 1
+}
+map_int32_double {
+  key: 111
+  value: 1
+}
+map_bool_bool {
+  key: true
+  value: false
+}
+map_string_string {
+  key: "112"
+  value: "1"
+}
+map_int32_bytes {
+  key: 113
+  value: "\001\000\000\000"
+}
+map_int32_enum {
+  key: 114
+  value: MAP_ENUM_BAZ
+}
+map_int32_foreign_message {
+  key: 115
+  value {
+    c: 1
+  }
+}