Use context manager to manage OS environment in tests

test/make_global_settings/ar/gyptest-make_global_settings_ar.py

 #!/usr/bin/env python
 
 # Copyright (c) 2014 Google Inc. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 Verifies 'AR' in make_global_settings.
 """
 
@@ skipping 83 matching lines @@
 test.run_gyp('make_global_settings_ar.gyp',
              '-Dcustom_ar_target=my_ar_target1',
              '-Dcustom_ar_host=my_ar_host1')
 # TODO(yukawa): Support 'AR'/'AR.host' in Ninja generator
 if test.format == 'make':
   verify_ar_target(test, ar='my_ar_target1', rel_path=True)
   verify_ar_host(test, ar='my_ar_host1', rel_path=True)
 
 
 # Test $AR and $AR_host environment variables.
-try:
-  os.environ['AR'] = 'my_ar_target2'
-  os.environ['AR_host'] = 'my_ar_host2'
+with TestGyp.LocalEnv({'AR': 'my_ar_target2',
+                       'AR_host': 'my_ar_host2'}):
   test.run_gyp('make_global_settings_ar.gyp')
-finally:
-  del os.environ['AR']
-  del os.environ['AR_host']
 # Ninja generator resolves $AR in gyp phase. Make generator doesn't.
 if test.format == 'ninja':
   if sys.platform == 'win32':
     # TODO(yukawa): Make sure if this is an expected result or not.
     verify_ar_target(test, ar='lib.exe', rel_path=False)
   else:
     verify_ar_target(test, ar='my_ar_target2', rel_path=False)
 verify_ar_host(test, ar='my_ar_host2', rel_path=False)
 
 
 # Test 'AR' in 'make_global_settings' with $AR_host environment variable.
-try:
-  os.environ['AR_host'] = 'my_ar_host3'
+with TestGyp.LocalEnv({'AR_host': 'my_ar_host3'}):
   test.run_gyp('make_global_settings_ar.gyp',
                '-Dcustom_ar_target=my_ar_target3')
-finally:
-  del os.environ['AR_host']
 # TODO(yukawa): Support 'AR' in Ninja generator
 if test.format == 'make':
   verify_ar_target(test, ar='my_ar_target3', rel_path=True)
 verify_ar_host(test, ar='my_ar_host3', rel_path=False)
 
 
 test.pass_test()