[Swarming] Correctly handle test262 archiving for local checkouts.

BUG=chromium:535160,v8:4792
LOG=n
TBR=tandrii@chromium.org, jkummerow@chromium.org

Review URL: https://codereview.chromium.org/1741383002

Cr-Commit-Position: refs/heads/master@{#34348}

test/test262/testcfg.py

@@ -39,7 +39,8 @@ from testrunner.local import testsuite
 from testrunner.local import utils
 from testrunner.objects import testcase
 
-ARCHIVE = os.path.join(os.path.dirname(os.path.abspath(__file__)), "data.tar")
+DATA = os.path.join(os.path.dirname(os.path.abspath(__file__)), "data")
+ARCHIVE = DATA + ".tar"
 
 TEST_262_HARNESS_FILES = ["sta.js", "assert.js"]
 
@@ -203,7 +204,7 @@ class Test262TestSuite(testsuite.TestSuite):
 
     # The archive is created only on swarming. Local checkouts have the
     # data folder.
-    if os.path.exists(ARCHIVE):
+    if os.path.exists(ARCHIVE) and not os.path.exists(DATA):
       print "Extracting archive..."
       tar = tarfile.open(ARCHIVE)
       tar.extractall(path=os.path.dirname(ARCHIVE))