IPRO+MPD: Make In-Place-Resource-Optimization with MapProxyDomain work

Fixes https://github.com/pagespeed/ngx_pagespeed/issues/1015

Pull with MPS Side for this change:
https://github.com/pagespeed/mod_pagespeed/pull/1161

src/ngx_base_fetch.cc

@@ -111,6 +111,8 @@ const char* BaseFetchTypeToCStr(NgxBaseFetchType type) {
       return "admin page";
     case kIproLookup:
       return "ipro lookup";
+    case kPageSpeedProxy:
+      return "pagespeed proxy";
   }
   CHECK(false);
   return "can't get here";