code: func New() IsolatedFake {
  	s := &isolatedFake{
  		mux:      http.NewServeMux(),
  		contents: map[string]map[isolated.HexDigest][]byte{},
  		staging:  map[string]map[isolated.HexDigest][]byte{},
  	}
  
  	s.handleJSON("/_ah/api/isolateservice/v1/server_details", s.serverDetails)
  	s.handleJSON("/_ah/api/isolateservice/v1/preupload", s.preupload)
  	s.handleJSON("/_ah/api/isolateservice/v1/finalize_gs_upload", s.finalizeGSUpload)
  	s.handleJSON("/_ah/api/isolateservice/v1/store_inline", s.storeInline)
  	s.handleJSON("/_ah/api/isolateservice/v1/retrieve", s.retrieve)
  	s.mux.HandleFunc("/fake/cloudstorage/upload", s.fakeCloudStorageUpload)
  	s.mux.HandleFunc("/fake/cloudstorage/download", s.fakeCloudStorageDownload)
  
  	// Fail on anything else.
  	s.mux.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
  		s.Fail(fmt.Errorf("unknown endpoint %q", req.URL))
  	})
  	return s
  }
docs: // New create a HTTP router that implements an isolated server.