Detach ArrayBuffer in test262

New incoming test262 tests check what happens on detached ("neutered")
ArrayBuffers. This patch makes the test262 infrastructure define
detaching an ArrayBuffer in terms of %ArrayBufferNeuter, passing the
--allow-natives-syntax flag, when it is needed.

BUG=v8:4193
LOG=N
R=adamk,machenbach

Review URL: https://codereview.chromium.org/1897203003

Cr-Commit-Position: refs/heads/master@{#35676}

test/test262/detachArrayBuffer.js

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+function $DETACHBUFFER(buffer) {
+  %ArrayBufferNeuter(buffer);
+}

test/test262/testcfg.py

@@ -43,6 +43,7 @@ DATA = os.path.join(os.path.dirname(os.path.abspath(__file__)), "data")
 ARCHIVE = DATA + ".tar"
 
 TEST_262_HARNESS_FILES = ["sta.js", "assert.js"]
+TEST_262_NATIVE_FILES = ["detachArrayBuffer.js"]
 
 TEST_262_SUITE_PATH = ["data", "test"]
 TEST_262_HARNESS_PATH = ["data", "harness"]
@@ -131,7 +132,12 @@ class Test262TestSuite(testsuite.TestSuite):
             self.GetIncludesForTest(testcase) + ["--harmony"] +
             (["--module"] if "module" in self.GetTestRecord(testcase) else []) +
             [os.path.join(self.testroot, testcase.path + ".js")] +
-            (["--throws"] if "negative" in self.GetTestRecord(testcase) else []))
+            (["--throws"] if "negative" in self.GetTestRecord(testcase)
+                          else []) +
+            (["--allow-natives-syntax"]
+             if "detachArrayBuffer.js" in
+                self.GetTestRecord(testcase).get("includes", [])
+             else []))
 
   def _VariantGeneratorFactory(self):
     return Test262VariantGenerator
@@ -159,11 +165,14 @@ class Test262TestSuite(testsuite.TestSuite):
                                              testcase.path)
     return testcase.test_record
 
+  def BasePath(self, filename):
+    return self.root if filename in TEST_262_NATIVE_FILES else self.harnesspath
+
   def GetIncludesForTest(self, testcase):
     test_record = self.GetTestRecord(testcase)
     if "includes" in test_record:
-      includes = [os.path.join(self.harnesspath, f)
-                  for f in test_record["includes"]]
+      return [os.path.join(self.BasePath(filename), filename)
+              for filename in test_record.get("includes", [])]
     else:
       includes = []
     return includes