Fix Win toolchain asset, fix script

BUG=skia:5764
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2351033004

Review-Url: https://codereview.chromium.org/2351033004

infra/bots/assets/asset_utils.py

@@ -38,6 +38,8 @@ TAG_PROJECT_SKIA = 'project:skia'
 TAG_VERSION_PREFIX = 'version:'
 TAG_VERSION_TMPL = '%s%%s' % TAG_VERSION_PREFIX
 
+WHICH = 'where' if sys.platform.startswith('win') else 'which'
+
 VERSION_FILENAME = 'VERSION'
 ZIP_BLACKLIST = ['.git', '.svn', '*.pyc', '.DS_STORE']
 
@@ -146,7 +148,10 @@ class CIPDStore(object):
 class GSStore(object):
   """Wrapper object for interacting with Google Storage."""
   def __init__(self, gsutil=None, bucket=DEFAULT_GS_BUCKET):
-    gsutil = os.path.abspath(gsutil) if gsutil else 'gsutil'
+    if gsutil:
+      gsutil = os.path.abspath(gsutil)
+    else:
+      gsutil = subprocess.check_output([WHICH, 'gsutil']).rstrip()
     self._gsutil = [gsutil]
     if gsutil.endswith('.py'):
       self._gsutil = ['python', gsutil]

infra/bots/assets/win_toolchain/VERSION

@@ -1 +1 @@
-1
+5