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

third_party/protobuf/java/core/src/main/java/com/google/protobuf/MapField.java

Index: third_party/protobuf/java/core/src/main/java/com/google/protobuf/MapField.java
diff --git a/third_party/protobuf/java/src/main/java/com/google/protobuf/MapField.java b/third_party/protobuf/java/core/src/main/java/com/google/protobuf/MapField.java
similarity index 99%
rename from third_party/protobuf/java/src/main/java/com/google/protobuf/MapField.java
rename to third_party/protobuf/java/core/src/main/java/com/google/protobuf/MapField.java
index b290993ca1ab76246e091615ece46c14e3ffc4a1..907f0f71120d6b0b29399c0e930ea602231b1aaf 100644
--- a/third_party/protobuf/java/src/main/java/com/google/protobuf/MapField.java
+++ b/third_party/protobuf/java/core/src/main/java/com/google/protobuf/MapField.java
@@ -93,15 +93,18 @@ public class MapField<K, V> implements MutabilityOracle {
       this.defaultEntry = defaultEntry;
     }
     
+    @Override
     public Message convertKeyAndValueToMessage(K key, V value) {
       return defaultEntry.newBuilderForType().setKey(key).setValue(value).buildPartial();
     }
     
+    @Override
     public void convertMessageToKeyAndValue(Message message, Map<K, V> map) {
       MapEntry<K, V> entry = (MapEntry<K, V>) message;
       map.put(entry.getKey(), entry.getValue());
     }
 
+    @Override
     public Message getMessageDefaultInstance() {
       return defaultEntry;
     }