Use swarming in run_lua CT task

ct/go/worker_scripts/run_lua/main.go

 // Application that runs lua scripts over the specified SKP repository.
 package main
 
 import (
         "flag"
-        "fmt"
         "io"
         "os"
+        "path"
         "path/filepath"
+        "strconv"
         "time"
 
         "github.com/skia-dev/glog"
 
         "go.skia.org/infra/ct/go/util"
         "go.skia.org/infra/ct/go/worker_scripts/worker_common"
         "go.skia.org/infra/go/common"
         skutil "go.skia.org/infra/go/util"
 )
 
 var (
-        workerNum     = flag.Int("worker_num", 1, "The number of this CT worker. It will be in the {1..100} range.")
+        startRange    = flag.Int("start_range", 1, "The number this worker will run lua scripts from.")
+        num           = flag.Int("num", 100, "The total number of SKPs to run on starting from the start_range.")
         pagesetType   = flag.String("pageset_type", util.PAGESET_TYPE_MOBILE_10k, "The type of pagesets to create from the Alexa CSV list. Eg: 10k, Mobile10k, All.")
         chromiumBuild = flag.String("chromium_build", "", "The chromium build that was used to create the SKPs we would like to run lua scripts against.")
         runID         = flag.String("run_id", "", "The unique run id (typically requester + timestamp).")
 )
 
 func main() {
         defer common.LogPanic()
         worker_common.Init()
         defer util.TimeTrack(time.Now(), "Running Lua Scripts")
         defer glog.Flush()
 
         if *chromiumBuild == "" {
                 glog.Error("Must specify --chromium_build")
                 return
         }
         if *runID == "" {
                 glog.Error("Must specify --run_id")
                 return
         }
 
-        // Create the task file so that the master knows this worker is still busy.
-        skutil.LogErr(util.CreateTaskFile(util.ACTIVITY_RUNNING_LUA_SCRIPTS))
-        defer util.DeleteTaskFile(util.ACTIVITY_RUNNING_LUA_SCRIPTS)
-
         // Sync Skia tree.
         skutil.LogErr(util.SyncDir(util.SkiaTreeDir))
 
         // Build tools.
         skutil.LogErr(util.BuildSkiaTools())
 
         // Instantiate GsUtil object.
         gs, err := util.NewGsUtil(nil)
         if err != nil {
                 glog.Error(err)
                 return
         }
 
         // Download SKPs if they do not exist locally.
-        if err := gs.DownloadWorkerArtifacts(util.SKPS_DIR_NAME, filepath.Join(*pagesetType, *chromiumBuild), *workerNum); err != nil {
+        localSkpsDir := filepath.Join(util.SkpsDir, *pagesetType, *chromiumBuild)
+        if _, err := gs.DownloadSwarmingArtifacts(localSkpsDir, util.SKPS_DIR_NAME, path.Join(*pagesetType, *chromiumBuild), *startRange, *num); err != nil {
                 glog.Error(err)
                 return
         }
-        localSkpsDir := filepath.Join(util.SkpsDir, *pagesetType, *chromiumBuild)
+        defer skutil.RemoveAll(localSkpsDir)
 
         // Download the lua script for this run from Google storage.
         luaScriptName := *runID + ".lua"
         luaScriptLocalPath := filepath.Join(os.TempDir(), luaScriptName)
         remoteDir := filepath.Join(util.LuaRunsDir, *runID)
         luaScriptRemotePath := filepath.Join(remoteDir, "scripts", luaScriptName)
         respBody, err := gs.GetRemoteFileContents(luaScriptRemotePath)
         if err != nil {
                 glog.Errorf("Could not fetch %s: %s", luaScriptRemotePath, err)
                 return
@@ skipping 37 matching lines @@
         err = util.ExecuteCmd(
                 filepath.Join(util.SkiaTreeDir, "out", "Release", util.BINARY_LUA_PICTURES), args,
                 []string{}, util.LUA_PICTURES_TIMEOUT, stdoutFile, stderrFile)
         if err != nil {
                 glog.Error(err)
                 return
         }
 
         // Copy stdout and stderr files to Google Storage.
         skutil.LogErr(
-                gs.UploadFile(stdoutFileName, os.TempDir(), filepath.Join(remoteDir, fmt.Sprintf("slave%d", *workerNum), "outputs")))
+                gs.UploadFile(stdoutFileName, os.TempDir(), filepath.Join(remoteDir, strconv.Itoa(*startRange), "outputs")))
         skutil.LogErr(
-                gs.UploadFile(stderrFileName, os.TempDir(), filepath.Join(remoteDir, fmt.Sprintf("slave%d", *workerNum), "errors")))
+                gs.UploadFile(stderrFileName, os.TempDir(), filepath.Join(remoteDir, strconv.Itoa(*startRange), "errors")))
 }