Extracted ICodedInputStream interface
diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
index b41a15d..7023d75 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
@@ -174,10 +174,10 @@
     public static TestMessageSet ParseDelimitedFrom(global::System.IO.Stream input, pb::ExtensionRegistry extensionRegistry) {

       return CreateBuilder().MergeDelimitedFrom(input, extensionRegistry).BuildParsed();

     }

-    public static TestMessageSet ParseFrom(pb::CodedInputStream input) {

+    public static TestMessageSet ParseFrom(pb::ICodedInputStream input) {

       return ((Builder) CreateBuilder().MergeFrom(input)).BuildParsed();

     }

-    public static TestMessageSet ParseFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+    public static TestMessageSet ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();

     }

     public static Builder CreateBuilder() { return new Builder(); }

@@ -244,11 +244,11 @@
         return this;

       }

       

-      public override Builder MergeFrom(pb::CodedInputStream input) {

+      public override Builder MergeFrom(pb::ICodedInputStream input) {

         return MergeFrom(input, pb::ExtensionRegistry.Empty);

       }

       

-      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+      public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -374,10 +374,10 @@
     public static TestMessageSetContainer ParseDelimitedFrom(global::System.IO.Stream input, pb::ExtensionRegistry extensionRegistry) {

       return CreateBuilder().MergeDelimitedFrom(input, extensionRegistry).BuildParsed();

     }

-    public static TestMessageSetContainer ParseFrom(pb::CodedInputStream input) {

+    public static TestMessageSetContainer ParseFrom(pb::ICodedInputStream input) {

       return ((Builder) CreateBuilder().MergeFrom(input)).BuildParsed();

     }

-    public static TestMessageSetContainer ParseFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+    public static TestMessageSetContainer ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();

     }

     public static Builder CreateBuilder() { return new Builder(); }

@@ -446,11 +446,11 @@
         return this;

       }

       

-      public override Builder MergeFrom(pb::CodedInputStream input) {

+      public override Builder MergeFrom(pb::ICodedInputStream input) {

         return MergeFrom(input, pb::ExtensionRegistry.Empty);

       }

       

-      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+      public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -623,10 +623,10 @@
     public static TestMessageSetExtension1 ParseDelimitedFrom(global::System.IO.Stream input, pb::ExtensionRegistry extensionRegistry) {

       return CreateBuilder().MergeDelimitedFrom(input, extensionRegistry).BuildParsed();

     }

-    public static TestMessageSetExtension1 ParseFrom(pb::CodedInputStream input) {

+    public static TestMessageSetExtension1 ParseFrom(pb::ICodedInputStream input) {

       return ((Builder) CreateBuilder().MergeFrom(input)).BuildParsed();

     }

-    public static TestMessageSetExtension1 ParseFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+    public static TestMessageSetExtension1 ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();

     }

     public static Builder CreateBuilder() { return new Builder(); }

@@ -695,11 +695,11 @@
         return this;

       }

       

-      public override Builder MergeFrom(pb::CodedInputStream input) {

+      public override Builder MergeFrom(pb::ICodedInputStream input) {

         return MergeFrom(input, pb::ExtensionRegistry.Empty);

       }

       

-      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+      public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -849,10 +849,10 @@
     public static TestMessageSetExtension2 ParseDelimitedFrom(global::System.IO.Stream input, pb::ExtensionRegistry extensionRegistry) {

       return CreateBuilder().MergeDelimitedFrom(input, extensionRegistry).BuildParsed();

     }

-    public static TestMessageSetExtension2 ParseFrom(pb::CodedInputStream input) {

+    public static TestMessageSetExtension2 ParseFrom(pb::ICodedInputStream input) {

       return ((Builder) CreateBuilder().MergeFrom(input)).BuildParsed();

     }

-    public static TestMessageSetExtension2 ParseFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+    public static TestMessageSetExtension2 ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();

     }

     public static Builder CreateBuilder() { return new Builder(); }

@@ -921,11 +921,11 @@
         return this;

       }

       

-      public override Builder MergeFrom(pb::CodedInputStream input) {

+      public override Builder MergeFrom(pb::ICodedInputStream input) {

         return MergeFrom(input, pb::ExtensionRegistry.Empty);

       }

       

-      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+      public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1122,10 +1122,10 @@
         public static Item ParseDelimitedFrom(global::System.IO.Stream input, pb::ExtensionRegistry extensionRegistry) {

           return CreateBuilder().MergeDelimitedFrom(input, extensionRegistry).BuildParsed();

         }

-        public static Item ParseFrom(pb::CodedInputStream input) {

+        public static Item ParseFrom(pb::ICodedInputStream input) {

           return ((Builder) CreateBuilder().MergeFrom(input)).BuildParsed();

         }

-        public static Item ParseFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        public static Item ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();

         }

         public static Builder CreateBuilder() { return new Builder(); }

@@ -1197,11 +1197,11 @@
             return this;

           }

           

-          public override Builder MergeFrom(pb::CodedInputStream input) {

+          public override Builder MergeFrom(pb::ICodedInputStream input) {

             return MergeFrom(input, pb::ExtensionRegistry.Empty);

           }

           

-          public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+          public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -1352,10 +1352,10 @@
     public static RawMessageSet ParseDelimitedFrom(global::System.IO.Stream input, pb::ExtensionRegistry extensionRegistry) {

       return CreateBuilder().MergeDelimitedFrom(input, extensionRegistry).BuildParsed();

     }

-    public static RawMessageSet ParseFrom(pb::CodedInputStream input) {

+    public static RawMessageSet ParseFrom(pb::ICodedInputStream input) {

       return ((Builder) CreateBuilder().MergeFrom(input)).BuildParsed();

     }

-    public static RawMessageSet ParseFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+    public static RawMessageSet ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();

     }

     public static Builder CreateBuilder() { return new Builder(); }

@@ -1425,11 +1425,11 @@
         return this;

       }

       

-      public override Builder MergeFrom(pb::CodedInputStream input) {

+      public override Builder MergeFrom(pb::ICodedInputStream input) {

         return MergeFrom(input, pb::ExtensionRegistry.Empty);

       }

       

-      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+      public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;