Update //third_party/protobuf to version 3.

third_party/protobuf/js/test2.proto

 // 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
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 // copyright notice, this list of conditions and the following disclaimer
 // in the documentation and/or other materials provided with the
 // distribution.
 //     * Neither the name of Google Inc. nor the names of its
 // contributors may be used to endorse or promote products derived from
 // this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (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: kenton@google.com (Kenton Varda)
+syntax = "proto2";
 
+option java_package = "com.google.apps.jspb.proto";
+option java_multiple_files = true;
 
-package protobuf_unittest;
+package jspb.test;
 
-option py_generic_services = true;
-
-message TestBadIdentifiers {
+message TestExtensionsMessage {
+  optional int32 intfield = 1;
   extensions 100 to max;
 }
 
-// Make sure these reasonable extension names don't conflict with internal
-// variables.
-extend TestBadIdentifiers {
-  optional string message = 100 [default="foo"];
-  optional string descriptor = 101 [default="bar"];
-  optional string reflection = 102 [default="baz"];
-  optional string service = 103 [default="qux"];
+message ExtensionMessage {
+  extend TestExtensionsMessage {
+    optional ExtensionMessage ext_field = 100;
+  }
+  optional string ext1 = 1;
 }
 
-message AnotherMessage {}
-service AnotherService {}
+// Floating extensions are only supported when generating a _lib.js library.
+extend TestExtensionsMessage {
+  optional ExtensionMessage floating_msg_field = 101;
+  optional string floating_str_field = 102;
+}