[CT] Add ability to download to/upload from swarming GS dir with numerical subdirs

ct/go/util/constants.go

 package util
 
 import (
         "fmt"
         "path/filepath"
         "time"
 )
 
 const (
         NUM_WORKERS_PROD      int = 100
@@ skipping 166 matching lines @@
                 MASTER_SCRIPT_TIMEOUT_PADDING
 
         // Fix Archives
         // Setting a 1 day timeout since it may take a while to validate archives.
         FIX_ARCHIVES_TIMEOUT = 1 * 24 * time.Hour
 
         // Poller
         MAKE_ALL_TIMEOUT = 15 * time.Minute
 
         WEBHOOK_SALT_MSG = `For prod, set this file to the value of GCE metadata key webhook_request_salt or call webhook.MustInitRequestSaltFromMetadata() if running in GCE. For testing, run 'echo -n "notverysecret" | base64 -w 0 > /b/storage/webhook_salt.data' or call frontend.InitForTesting().`
+
+        // Swarming constants.
+        SWARMING_DIR_NAME = "swarming"
 )
 
 type PagesetTypeInfo struct {
         NumPages                   int
         CSVSource                  string
         UserAgent                  string
         CaptureArchivesTimeoutSecs int
         CreatePagesetsTimeoutSecs  int
         CaptureSKPsTimeoutSecs     int
         RunChromiumPerfTimeoutSecs int
@@ skipping 127 matching lines @@
 
         SupportedPageSetsToDesc = map[string]string{
                 PLATFORM_LINUX:   "Linux (100 Ubuntu12.04 machines)",
                 PLATFORM_ANDROID: "Android (100 N5 devices)",
         }
 )
 
 func NumWorkers() int {
         return len(Slaves)
 }