Update //third_party/protobuf to version 3.

third_party/protobuf/js/testempty.proto

Index: third_party/protobuf/js/testempty.proto
diff --git a/third_party/protobuf/src/google/protobuf/unittest_import_public.proto b/third_party/protobuf/js/testempty.proto
similarity index 87%
copy from third_party/protobuf/src/google/protobuf/unittest_import_public.proto
copy to third_party/protobuf/js/testempty.proto
index ea5d1b13fea77a432cecc0980664c020159d108a..960bce4e5c69c89a863d15f2490aa890bfa97766 100644
--- a/third_party/protobuf/src/google/protobuf/unittest_import_public.proto
+++ b/third_party/protobuf/js/testempty.proto
@@ -1,6 +1,6 @@
 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 Google Inc.  All rights reserved.
-// http://code.google.com/p/protobuf/
+// https://developers.google.com/protocol-buffers/
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
@@ -28,13 +28,7 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-// Author: liujisi@google.com (Pherl Liu)
+syntax = "proto2";
 
+package javatests.com.google.apps.jspb;
 
-package protobuf_unittest_import;
-
-option java_package = "com.google.protobuf.test";
-
-message PublicImportMessage {
-  optional int32 e = 1;
-}