Remove all support for cygwin in run-webkit-tests.

third_party/WebKit/Tools/Scripts/webkitpy/common/system/platform_info.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/common/system/platform_info.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/common/system/platform_info.py b/third_party/WebKit/Tools/Scripts/webkitpy/common/system/platform_info.py
index 1b2c3739c33ec1a33cf3741340771be5e5143dd3..700806774450f515e1b819acc4b03a718bfc8005 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/common/system/platform_info.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/common/system/platform_info.py
@@ -56,7 +56,7 @@ class PlatformInfo(object):
             self.os_version = self._determine_mac_version(platform_module.mac_ver()[0])
         if self.os_name.startswith('win'):
             self.os_version = self._determine_win_version(self._win_version_tuple(sys_module))
-        self._is_cygwin = sys_module.platform == 'cygwin'
+        assert sys.platform != 'cygwin', 'Cygwin is not supported.'
 
     def is_mac(self):
         return self.os_name == 'mac'
@@ -64,9 +64,6 @@ class PlatformInfo(object):
     def is_win(self):
         return self.os_name == 'win'
 
-    def is_cygwin(self):
-        return self._is_cygwin
-
     def is_linux(self):
         return self.os_name == 'linux'
 
@@ -139,7 +136,7 @@ class PlatformInfo(object):
             return 'mac'
         if sys_platform.startswith('linux'):
             return 'linux'
-        if sys_platform in ('win32', 'cygwin'):
+        if sys_platform == 'win32':
             return 'win'
         if sys_platform.startswith('freebsd'):
             return 'freebsd'