Bug 1373178 - use preflight mech to hide win 10 taskbar; r=jmaher

MozReview-Commit-ID: 7tYL7A8Cjqi

--HG--
extra : rebase_source : 908335275bb1c66bd571cee5b10bda909006d4c6

testing/mozharness/configs/unittests/win_taskcluster_unittest.py

@@ -260,7 +260,17 @@ config = {
             'architectures': ['32bit', '64bit'],
             'halt_on_failure': True,
             'enabled': ADJUST_MOUSE_AND_SCREEN
-        }
+        },
+        {
+            'name': 'hide win 10 taskbar',
+            'cmd': [
+                'powershell', '-command',
+                '"&{$p=\'HKCU:SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\StuckRects3\';$v=(Get-ItemProperty -Path $p).Settings;$v[8]=3;&Set-ItemProperty -Path $p -Name Settings -Value $v;&Stop-Process -ProcessName explorer}"'
+            ],
+            'architectures': ['32bit', '64bit'],
+            'halt_on_failure': True,
+            'enabled': os.environ.get('ProgramFiles(x86)', False)
+        },
     ],
     "vcs_output_timeout": 1000,
     "minidump_save_path": "%(abs_work_dir)s/../minidumps",