autotest: wifi: Remove WiFiInterfaceClaimContext

This wrapper can be easily replaced with a try-catch-finally block.

BUG=chromium:628791
TEST=Ran network_WiFi_ChannelScanDwellTime, its only consumer.

Change-Id: Ieec7a6cb6a6c1840c03f0647858291988ae3023a
Signed-off-by: Kirtika Ruchandani <kirtika@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1292792
Commit-Ready: Kirtika Ruchandani <kirtika@chromium.org>
Tested-by: Kirtika Ruchandani <kirtika@chromium.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
diff --git a/server/cros/network/wifi_interface_claim_context.py b/server/cros/network/wifi_interface_claim_context.py
deleted file mode 100644
index 4d5a95b..0000000
--- a/server/cros/network/wifi_interface_claim_context.py
+++ /dev/null
@@ -1,22 +0,0 @@
-# Copyright 2015 The Chromium OS Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-class WiFiInterfaceClaimContext(object):
-    """Context that encapsulates claiming of a wifi interface.
-
-    This context ensures that if the test fails while the interface is claimed
-    we will attempt to release it before our test exits.
-
-    """
-
-    def __init__(self, client):
-        self._client = client
-
-
-    def __enter__(self):
-        self._client.claim_wifi_if()
-
-
-    def __exit__(self, exception, value, traceback):
-        self._client.release_wifi_if()
diff --git a/server/site_tests/network_WiFi_ChannelScanDwellTime/network_WiFi_ChannelScanDwellTime.py b/server/site_tests/network_WiFi_ChannelScanDwellTime/network_WiFi_ChannelScanDwellTime.py
index bc5e62c..ec40e70 100644
--- a/server/site_tests/network_WiFi_ChannelScanDwellTime/network_WiFi_ChannelScanDwellTime.py
+++ b/server/site_tests/network_WiFi_ChannelScanDwellTime/network_WiFi_ChannelScanDwellTime.py
@@ -8,7 +8,6 @@
 
 from autotest_lib.server.cros.network import frame_sender
 from autotest_lib.server.cros.network import hostap_config
-from autotest_lib.server.cros.network import wifi_interface_claim_context
 from autotest_lib.server import site_linux_system
 from autotest_lib.client.common_lib import error
 from autotest_lib.client.common_lib import utils
@@ -186,11 +185,13 @@
         # will prevent shill and wpa_supplicant from managing that interface.
         # So this test can have the sole ownership of the interface and can
         # perform scans without interference from shill and wpa_supplicant.
-        with wifi_interface_claim_context.WiFiInterfaceClaimContext(
-                self.context.client):
+        self.context.client.claim_wifi_if()
+        try:
             # Get channel dwell time for single-channel scan
             dwell_time = self._channel_dwell_time_test(True)
             logging.info('Channel dwell time for single-channel scan: %d ms',
                          dwell_time)
             self.write_perf_keyval(
                     {'dwell_time_single_channel_scan': dwell_time})
+        finally:
+            self.context.client.release_wifi_if()