Update third_party/protobuf to protobuf-v3.0.0-beta-3

third_party/protobuf/python/google/protobuf/internal/descriptor_pool_test2.proto

 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 Google Inc.  All rights reserved.
 // 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.
@@ skipping 15 matching lines @@
 // 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.
 
 syntax = "proto2";
 
 package google.protobuf.python.internal;
 
 import "google/protobuf/internal/descriptor_pool_test1.proto";
+import public "google/protobuf/internal/more_messages.proto";
 
 
 message DescriptorPoolTest3 {
 
   extend DescriptorPoolTest1 {
     optional DescriptorPoolTest3 descriptor_pool_test = 1001;
   }
 
   enum NestedEnum {
     NU = 13;
@@ skipping 17 matching lines @@
         SIGMA = 18;
       }
       optional NestedEnum nested_enum = 1 [default = RHO];
       optional string nested_field = 2 [default = "sigma"];
     }
   }
 
   optional NestedMessage nested_message = 2;
 }