Fully converted over to ICodedOutputStream for all WriteTo derivations
diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
index ecf92cf..b00ff2f 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
@@ -106,7 +106,7 @@
       }

     }

     

-    public override void WriteTo(pb::CodedOutputStream output) {

+    public override void WriteTo(pb::ICodedOutputStream output) {

       int size = SerializedSize;

       if (HasD) {

         output.WriteInt32(1, "d", D);