Update //third_party/protobuf to version 3.

third_party/protobuf/src/google/protobuf/unittest_drop_unknown_fields.proto

Index: third_party/protobuf/src/google/protobuf/unittest_drop_unknown_fields.proto
diff --git a/third_party/protobuf/src/google/protobuf/unittest_no_generic_services.proto b/third_party/protobuf/src/google/protobuf/unittest_drop_unknown_fields.proto
similarity index 75%
copy from third_party/protobuf/src/google/protobuf/unittest_no_generic_services.proto
copy to third_party/protobuf/src/google/protobuf/unittest_drop_unknown_fields.proto
index cffb4122c5c4f9d2e63a09d70c3784614617d88d..8aa3a37b8e29a085c6f78cd0d5d05a82c6cf9c5d 100644
--- a/third_party/protobuf/src/google/protobuf/unittest_no_generic_services.proto
+++ b/third_party/protobuf/src/google/protobuf/unittest_drop_unknown_fields.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
@@ -28,25 +28,31 @@
 // (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 = "proto3";
 
-package google.protobuf.no_generic_services_test;
+package unittest_drop_unknown_fields;
+option objc_class_prefix = "DropUnknowns";
 
-// *_generic_services are false by default.
+option csharp_namespace = "Google.Protobuf.TestProtos";
 
-message TestMessage {
-  optional int32 a = 1;
-  extensions 1000 to max;
+message Foo {
+  enum NestedEnum {
+    FOO = 0;
+    BAR = 1;
+    BAZ = 2;
+  }
+  int32 int32_value = 1;
+  NestedEnum enum_value = 2;
 }
 
-enum TestEnum {
-  FOO = 1;
-}
-
-extend TestMessage {
-  optional int32 test_extension = 1000;
-}
-
-service TestService {
-  rpc Foo(TestMessage) returns(TestMessage);
+message FooWithExtraFields {
+  enum NestedEnum {
+    FOO = 0;
+    BAR = 1;
+    BAZ = 2;
+    QUX = 3;
+  }
+  int32 int32_value = 1;
+  NestedEnum enum_value = 2;
+  int32 extra_int32_value = 3;
 }