Update //third_party/protobuf to version 3.

third_party/protobuf/java/src/main/java/com/google/protobuf/Extension.java

Index: third_party/protobuf/java/src/main/java/com/google/protobuf/Extension.java
diff --git a/third_party/protobuf/src/google/protobuf/unittest_mset.proto b/third_party/protobuf/java/src/main/java/com/google/protobuf/Extension.java
similarity index 52%
copy from third_party/protobuf/src/google/protobuf/unittest_mset.proto
copy to third_party/protobuf/java/src/main/java/com/google/protobuf/Extension.java
index 3497f09fa6d41b7b38357e7f2610dfb5c087d3e4..68d29f33d47b43ffaa1253903a5e12b1c3bb6f41 100644
--- a/third_party/protobuf/src/google/protobuf/unittest_mset.proto
+++ b/third_party/protobuf/java/src/main/java/com/google/protobuf/Extension.java
@@ -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
@@ -28,45 +28,58 @@
 // (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)
-//  Based on original Protocol Buffers design by
-//  Sanjay Ghemawat, Jeff Dean, and others.
-//
-// This file contains messages for testing message_set_wire_format.
+package com.google.protobuf;
 
-package protobuf_unittest;
+/**
+ * Interface that generated extensions implement.
+ *
+ * @author liujisi@google.com (Jisi Liu)
+ */
+public abstract class Extension<ContainingType extends MessageLite, Type>
+    extends ExtensionLite<ContainingType, Type> {
 
-option optimize_for = SPEED;
+  /** Returns the descriptor of the extension. */
+  public abstract Descriptors.FieldDescriptor getDescriptor();
 
-// A message with message_set_wire_format.
-message TestMessageSet {
-  option message_set_wire_format = true;
-  extensions 4 to max;
-}
+  /** Returns whether or not this extension is a Lite Extension. */
+  final boolean isLite() {
+    return false;
+  }
 
-message TestMessageSetContainer {
-  optional TestMessageSet message_set = 1;
-}
+  // All the methods below are extension implementation details.
 
-message TestMessageSetExtension1 {
-  extend TestMessageSet {
-    optional TestMessageSetExtension1 message_set_extension = 1545008;
+  /**
+   * The API type that the extension is used for.
+   */
+  protected enum ExtensionType {
+    IMMUTABLE,
+    MUTABLE,
+    PROTO1,
   }
-  optional int32 i = 15;
-}
 
-message TestMessageSetExtension2 {
-  extend TestMessageSet {
-    optional TestMessageSetExtension2 message_set_extension = 1547769;
+  protected ExtensionType getExtensionType() {
+    // TODO(liujisi): make this abstract after we fix proto1.
+    return ExtensionType.IMMUTABLE;
   }
-  optional string str = 25;
-}
 
-// MessageSet wire format is equivalent to this.
-message RawMessageSet {
-  repeated group Item = 1 {
-    required int32 type_id = 2;
-    required bytes message = 3;
+  /**
+   * Type of a message extension.
+   */
+  public enum MessageType {
+    PROTO1,
+    PROTO2,
+  }
+  
+  /**
+   * If the extension is a message extension (i.e., getLiteType() == MESSAGE),
+   * returns the type of the message, otherwise undefined.
+   */
+  public MessageType getMessageType() {
+    return MessageType.PROTO2;
   }
-}
 
+  protected abstract Object fromReflectionType(Object value);
+  protected abstract Object singularFromReflectionType(Object value);
+  protected abstract Object toReflectionType(Object value);
+  protected abstract Object singularToReflectionType(Object value);
+}