Blimp: change logger to use switch/case for types.

blimp/common/proto/render_widget.proto

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 package blimp;
 
 message RenderWidgetMessage {
   enum Type {
+    UNKNOWN = 0;
+
     // Engine => Client types.
     INITIALIZE = 1;
     CREATED = 2;
     DELETED = 3;
   }
 
-  optional Type type = 1;
+  optional Type type = 1 [default = UNKNOWN];
   optional int32 render_widget_id = 2;
-}
+}