[bigint] Enable test262's BigInt tests.

Bug: v8:6791
Cq-Include-Trybots: master.tryserver.v8:v8_linux_noi18n_rel_ng
Change-Id: I4a8aebe68617a75fa5ab9778bfa1f2ca561e9aef
Reviewed-on: https://chromium-review.googlesource.com/756841
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49900}

test/test262/test262.status

@@ -514,6 +514,9 @@
   'harness/detachArrayBuffer': [SKIP],
   'harness/detachArrayBuffer-host-detachArrayBuffer': [SKIP],
 
+  # Bogus test. Already fixed upstream.
+  'built-ins/BigInt/prototype/toString/length': [FAIL],
+
   ############################ SKIPPED TESTS #############################
 
   # These tests take a looong time to run.

test/test262/testcfg.py

@@ -42,12 +42,13 @@ from testrunner.objects import testcase
 # TODO(littledan): move the flag mapping into the status file
 FEATURE_FLAGS = {
   'async-iteration': '--harmony-async-iteration',
+  'BigInt': '--harmony-bigint',
   'regexp-named-groups': '--harmony-regexp-named-captures',
   'regexp-unicode-property-escapes': '--harmony-regexp-property',
   'Promise.prototype.finally': '--harmony-promise-finally',
 }
 
-SKIPPED_FEATURES = set(['BigInt', 'class-fields', 'optional-catch-binding'])
+SKIPPED_FEATURES = set(['class-fields', 'optional-catch-binding'])
 
 DATA = os.path.join(os.path.dirname(os.path.abspath(__file__)), "data")
 ARCHIVE = DATA + ".tar"