Update //third_party/protobuf to version 3.

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

Index: third_party/protobuf/java/src/main/java/com/google/protobuf/MutabilityOracle.java
diff --git a/third_party/protobuf/src/google/protobuf/unittest_lite_imports_nonlite.proto b/third_party/protobuf/java/src/main/java/com/google/protobuf/MutabilityOracle.java
similarity index 77%
copy from third_party/protobuf/src/google/protobuf/unittest_lite_imports_nonlite.proto
copy to third_party/protobuf/java/src/main/java/com/google/protobuf/MutabilityOracle.java
index d52cb8cc36d8924a3454f9170f6b338f14a59c5c..82b723c95df602e9ab2e403e1141fce6ebb01b6d 100644
--- a/third_party/protobuf/src/google/protobuf/unittest_lite_imports_nonlite.proto
+++ b/third_party/protobuf/java/src/main/java/com/google/protobuf/MutabilityOracle.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
@@ -28,16 +28,21 @@
 // (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)
-//
-// Tests that a "lite" message can import a regular message.
-
-package protobuf_unittest;
-
-import "google/protobuf/unittest.proto";
+package com.google.protobuf;
 
-option optimize_for = LITE_RUNTIME;
+/**
+ * Verifies that an object is mutable, throwing if not.
+ */
+interface MutabilityOracle {
+  static final MutabilityOracle IMMUTABLE = new MutabilityOracle() {
+    @Override
+    public void ensureMutable() {
+      throw new UnsupportedOperationException();
+    }
+  };
 
-message TestLiteImportsNonlite {
-  optional TestAllTypes message = 1;
+  /**
+   * Throws an {@link UnsupportedOperationException} if not mutable.
+   */
+  void ensureMutable();
 }