Added ToBuilder and WeakToBuilder
diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
index 5af7fd8..8aca399 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
@@ -146,6 +146,7 @@
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestEmbedOptimizedForSize prototype) {
       return (Builder) new Builder().MergeFrom(prototype);