Update //third_party/protobuf to version 3.

third_party/protobuf/javanano/src/test/java/com/google/protobuf/nano/unittest_extension_nano.proto

Index: third_party/protobuf/javanano/src/test/java/com/google/protobuf/nano/unittest_extension_nano.proto
diff --git a/third_party/protobuf/javanano/src/test/java/com/google/protobuf/nano/unittest_extension_nano.proto b/third_party/protobuf/javanano/src/test/java/com/google/protobuf/nano/unittest_extension_nano.proto
new file mode 100644
index 0000000000000000000000000000000000000000..ca56b3dd45477af1cde0e5b143cfa8532807cdf6
--- /dev/null
+++ b/third_party/protobuf/javanano/src/test/java/com/google/protobuf/nano/unittest_extension_nano.proto
@@ -0,0 +1,37 @@
+syntax = "proto2";
+
+option java_outer_classname = "Extensions";
+option java_package = "com.google.protobuf.nano.testext";
+
+message ExtendableMessage {
+  optional int32 field = 1;
+  extensions 10 to max;
+}
+
+enum AnEnum {
+  FIRST_VALUE = 1;
+  SECOND_VALUE = 2;
+}
+
+message AnotherMessage {
+  optional string string = 1;
+  optional bool value = 2;
+  repeated int32 integers = 3;
+}
+
+message ContainerMessage {
+  extend ExtendableMessage {
+    optional bool another_thing = 100;
+    // The largest permitted field number, per
+    // https://developers.google.com/protocol-buffers/docs/proto#simple
+    optional bool large_field_number = 536870911;
+  }
+}
+
+// For testNanoOptionalGroupWithUnknownFieldsEnabled;
+// not part of the extensions tests.
+message MessageWithGroup {
+  optional group Group = 1 {
+    optional int32 a = 2;
+  }
+}