Reset chromium checkout before syncing

ct/go/worker_scripts/fix_archives/main.go

 // fix_archives is an application that validates the webpage archives of a
 // pageset type and deletes the archives which are found to be deliver
 // inconsistent benchmark results.
 // See https://code.google.com/p/chromium/issues/detail?id=456883 for more
 // details.
 package main
 
 import (
         "encoding/csv"
         "flag"
@@ skipping 42 matching lines @@
         }
         if *chromiumBuild == "" {
                 glog.Error("Must specify --chromium_build")
                 return
         }
         if *runID == "" {
                 glog.Error("Must specify --run_id")
                 return
         }
 
+        // Reset the local chromium checkout.
+        if err := util.ResetCheckout(util.ChromiumSrcDir); err != nil {
+                glog.Errorf("Could not reset %s: %s", util.ChromiumSrcDir, err)
+                return
+        }
         // Sync the local chromium checkout.
         if err := util.SyncDir(util.ChromiumSrcDir); err != nil {
                 glog.Errorf("Could not gclient sync %s: %s", util.ChromiumSrcDir, err)
                 return
         }
 
         // Instantiate GsUtil object.
         gs, err := util.NewGsUtil(nil)
         if err != nil {
                 glog.Error(err)
@@ skipping 192 matching lines @@
         reader.FieldsPerRecord = -1
         rawCSVdata, err := reader.ReadAll()
         if err != nil {
                 return nil, nil, fmt.Errorf("Could not read %s: %s", csvPath, err)
         }
         if len(rawCSVdata) != 2 {
                 return nil, nil, fmt.Errorf("No data in %s", csvPath)
         }
         return rawCSVdata[0], rawCSVdata[1], nil
 }