[alerts-dispatcher] update to build again :) also fixes a concurrent map access

go/src/infra/monitoring/looper/looper.go

 package looper
 
 import (
         "expvar"
         "time"
 
         "github.com/luci/luci-go/common/clock"
         "github.com/luci/luci-go/common/logging"
         "golang.org/x/net/context"
 )
@@ skipping 51 matching lines @@
                         expvars.Add("Errors", 1)
                         if consecErrs++; consecErrs >= maxErrs {
                                 ret.Success = false
                                 return
                         }
                 } else {
                         consecErrs = 0
                 }
 
                 nextCycle = cycle - dur
-                tmr.Reset(nextCycle)
+                if tmr.Reset(nextCycle) {
+                        log.Errorf("Timer was still active")
+                }
         }
 
         // Run f at least once.
         run()
 
         // Keep running f until ctx is done.
         for {
-                if ar := <-tmr.GetC(); ar.Incomplete() {
+                select {
+                case <-ctx.Done():
+                        tmr.Stop()
                         return ret
-                }
-                run()
-                if !ret.Success {
-                        return ret
+                case <-tmr.GetC():
+                        run()
+                        if !ret.Success {
+                                return ret
+                        }
                 }
         }
 }