Convert sbox_validation_tests to run exclusively on Swarming

0 configs already ran on Swarming
7 used to run locally and were converted:
- chromium.fyi.json: CrWinAsan tester
- chromium.fyi.json: CrWinAsan(dll) tester
- chromium.win.json: Vista Tests (1)
- chromium.win.json: Win 7 Tests x64 (1)
- chromium.win.json: Win7 Tests (1)
- chromium.win.json: Win7 Tests (dbg)(1)
- chromium.win.json: XP Tests (1)

Ran:
  ./manage.py --convert sbox_validation_tests

R=cpu@chromium.org,thakis@chromium.org
BUG=98637

Review URL: https://codereview.chromium.org/1212003003

Cr-Original-Commit-Position: refs/heads/master@{#338434}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 59ef9be12ee89bc452b83bec060d90514dc86c66

gn_migration.gypi

@@ -570,6 +570,7 @@
               'dependencies': [
                 '../sandbox/sandbox.gyp:sbox_integration_tests',
                 '../sandbox/sandbox.gyp:sbox_unittests',
+                '../sandbox/sandbox.gyp:sbox_validation_tests',
               ],
             }],
             ['use_ash==1', {