Reverts third_party/protobuf: Update to HEAD (f52e188fe4)

third_party/protobuf/objectivec/Tests/GPBUnknownFieldSetTest.m

Index: third_party/protobuf/objectivec/Tests/GPBUnknownFieldSetTest.m
diff --git a/third_party/protobuf/objectivec/Tests/GPBUnknownFieldSetTest.m b/third_party/protobuf/objectivec/Tests/GPBUnknownFieldSetTest.m
index b2b5b21e6175a4108f2bd025469b2504a3ba0d72..01217ca61a3ab96d621311657cbcb76ac87ecf8b 100644
--- a/third_party/protobuf/objectivec/Tests/GPBUnknownFieldSetTest.m
+++ b/third_party/protobuf/objectivec/Tests/GPBUnknownFieldSetTest.m
@@ -60,6 +60,10 @@
   unknownFields_ = emptyMessage_.unknownFields;
 }
 
+- (GPBUnknownField *)getField:(int32_t)number {
+  return [unknownFields_ getField:number];
+}
+
 // Constructs a protocol buffer which contains fields with all the same
 // numbers as allFieldsData except that each field is some other wire
 // type.