Activate network traffic annotation tests on Windows trybot.

Network traffic annotation test on win7_chromium_rel_ng is activated.

Bug: 690323
Change-Id: Ic3dcba34e9898b7a4f71067f5531db1952f19c9a
Reviewed-on: https://chromium-review.googlesource.com/781461Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Martin Šrámek <msramek@chromium.org>
Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539000}

tools/traffic_annotation/scripts/check_annotations.py

@@ -17,7 +17,7 @@ import sys
 # If this test starts failing, please set TEST_IS_ENABLED to "False" and file a
 # bug to get this reenabled, and cc the people listed in
 # //tools/traffic_annotation/OWNERS.
-TEST_IS_ENABLED = sys.platform != 'win32'
+TEST_IS_ENABLED = True
 
 
 class NetworkTrafficAnnotationChecker():