Update //third_party/protobuf to version 3.

third_party/protobuf/objectivec/GPBRootObject.h

Index: third_party/protobuf/objectivec/GPBRootObject.h
diff --git a/third_party/protobuf/src/google/protobuf/unittest_import_public_lite.proto b/third_party/protobuf/objectivec/GPBRootObject.h
similarity index 80%
copy from third_party/protobuf/src/google/protobuf/unittest_import_public_lite.proto
copy to third_party/protobuf/objectivec/GPBRootObject.h
index d077563cbd84d7be6daddec3f553cb564f23da0a..e2af5d974837a58ec4a2ba7d1d0d020e2ea16d92 100644
--- a/third_party/protobuf/src/google/protobuf/unittest_import_public_lite.proto
+++ b/third_party/protobuf/objectivec/GPBRootObject.h
@@ -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
@@ -28,15 +28,19 @@
 // (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)
+#import <Foundation/Foundation.h>
 
+@class GPBExtensionRegistry;
 
-package protobuf_unittest_import;
+NS_ASSUME_NONNULL_BEGIN
 
-option optimize_for = LITE_RUNTIME;
+// All Root Objects derive from GPBRootObject. It supplies a registry
+// for derived classes to register their extensions to.
+@interface GPBRootObject : NSObject
 
-option java_package = "com.google.protobuf";
+// Per class registry.
++ (GPBExtensionRegistry *)extensionRegistry;
 
-message PublicImportMessageLite {
-  optional int32 e = 1;
-}
+@end
+
+NS_ASSUME_NONNULL_END