Set /SUBSYSTEM down to 5.02 on x64 to more closely match x86

This makes us get XP/Server 2003 compatible metrics for window
sizes and so indirectly fixes pixels being cut off at the top
of the window.

(Server 2003 compatible metrics make us match x86 behaviour, and
since we need to maintain XP subsystem there indefinitely, I can
sort of rationalize it on that basis.)

R=jschuh@chromium.org, wfh@chromium.org
BUG=361720

Review URL: https://codereview.chromium.org/311953003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274853 0039d316-1c4b-4281-b951-d872f2087c98

build/common.gypi

@@ -2973,6 +2973,9 @@
         'msvs_configuration_platform': 'x64',
         'msvs_settings': {
           'VCLinkerTool': {
+            # Make sure to understand http://crbug.com/361720 if you want to
+            # increase this.
+            'MinimumRequiredVersion': '5.02',  # Server 2003.
             'TargetMachine': '17', # x86 - 64
             'AdditionalLibraryDirectories!':
               ['<(windows_sdk_path)/Lib/win8/um/x86'],