Added a Python script in tools/ to generate IDN test cases.

components/url_formatter/url_formatter_unittest.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/url_formatter/url_formatter.h"
 
 #include <stddef.h>
 #include <string.h>
 
 #include <vector>
@@ skipping 20 matching lines @@
   const char* const input;
   // The equivalent Unicode version of the domain. Even if we expect the domain
   // to be displayed in Punycode, this should still contain the Unicode
   // equivalent (see |unicode_allowed|).
   const wchar_t* unicode_output;
   // Whether we expect the domain to be displayed decoded as a Unicode string
   // (true) or in its Punycode form (false).
   const bool unicode_allowed;
 };
 
+// These cases can be generated with the script
+// tools/security/idn_test_case_generator.py.
+// See documentation there: you can either run it from the command line or call
+// the make_case function directly from the Python shell (which may be easier
+// for entering Unicode text).
+//
+// Q: Why not just do this conversion right here in the test, rather than having
+//    a Python script to generate it?
+// A: Because then we would have to rely on complex logic (IDNA encoding) in the
+//    test itself; the same code we are trying to test. By using Python's IDN
+//    encoder to generate the test data, we independently verify that our
+//    algorithm is correct.
+
 // TODO(jshin): Replace L"..." with "..." in UTF-8 when it's easier to read.
 const IDNTestCase idn_cases[] = {
   // No IDN
   {"www.google.com", L"www.google.com", true},
   {"www.google.com.", L"www.google.com.", true},
   {".", L".", true},
   {"", L"", true},
   // IDN
   // Hanzi (Traditional Chinese)
   {"xn--1lq90ic7f1rc.cn", L"\x5317\x4eac\x5927\x5b78.cn", true},
@@ skipping 952 matching lines @@
     0, kNpos, kNpos, kNpos, kNpos, kNpos, kNpos, 0, kNpos, kNpos, kNpos, kNpos,
     0, 1, 2, 3, 4, 5, 6, 7
   };
   CheckAdjustedOffsets("http://user@foo.com/", kFormatUrlOmitAll,
                        net::UnescapeRule::NORMAL, omit_all_offsets);
 }
 
 }  // namespace
 
 }  // namespace url_formatter