Add shell=True for gn-format.py on Windows

Broken if gn.exe isn't in path (which it isn't if you're using the
depot_tools wrapper goop.)

Review URL: https://codereview.chromium.org/1892213002

Cr-Original-Commit-Position: refs/heads/master@{#387689}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 3a93fa5a544dc594288a725b34e6ecda8c718802

tools/gn/bin/gn-format.py

diff --git a/tools/gn/bin/gn-format.py b/tools/gn/bin/gn-format.py
index c835753..4769640 100644
--- a/tools/gn/bin/gn-format.py
+++ b/tools/gn/bin/gn-format.py
@@ -38,7 +38,7 @@
   p = subprocess.Popen([binary, 'format', '--stdin'],
                        stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                        stdin=subprocess.PIPE, startupinfo=startupinfo,
-                       universal_newlines=True)
+                       shell=True, universal_newlines=True)
   stdout, stderr = p.communicate(input=text)
   if p.returncode != 0:
     print 'Formatting failed, please report to gn-dev@chromium.org.'