[milo] Refactor all html knowledge out of backends.

milo/frontend/view_config.go

 // Copyright 2015 The LUCI Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //      http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
 package frontend
 
 import (
         "net/http"
 
         "cloud.google.com/go/datastore"
         "google.golang.org/appengine"
 
+        "github.com/luci/luci-go/common/errors"
         "github.com/luci/luci-go/common/logging"
         "github.com/luci/luci-go/milo/common"
         "github.com/luci/luci-go/server/router"
         "github.com/luci/luci-go/server/templates"
 )
 
 // ConfigsHandler renders the page showing the currently loaded set of luci-configs.
 func ConfigsHandler(c *router.Context) {
         projects, err := common.GetAllProjects(c.Context)
         if err != nil {
-                common.ErrorPage(
-                        c, http.StatusInternalServerError,
-                        "Error while getting projects: "+err.Error())
+                ErrorHandler(c, errors.Annotate(err, "Error while getting projects").Err())
                 return
         }
         sc, err := common.GetCurrentServiceConfig(c.Context)
         if err != nil && err != datastore.ErrNoSuchEntity {
-                common.ErrorPage(
-                        c, http.StatusInternalServerError,
-                        "Error while getting service config: "+err.Error())
+                ErrorHandler(c, errors.Annotate(err, "Error while getting service config").Err())
                 return
         }
 
         templates.MustRender(c.Context, c.Writer, "pages/configs.html", templates.Args{
                 "Projects":      projects,
                 "ServiceConfig": sc,
         })
 }
 
 // UpdateHandler is an HTTP handler that handles configuration update requests.
@@ skipping 14 matching lines @@
                         logging.WithError(servErr).Errorf(
                                 c, "pubsub subscriber handler encountered error")
                 }
         }
         if projErr != nil || servErr != nil {
                 h.WriteHeader(http.StatusInternalServerError)
                 return
         }
         h.WriteHeader(http.StatusOK)
 }