download_from_google_storage: Use vpython3 instead of vpython

We have vpython wheels for py3 but not for py2 on mac/arm. With this,
download_from_google_storage.py works on arm mac even without the
vpython bypass. (Also, moving from py2 to py3 seems like a good thing
in general.)

Bug: 1205263,1103236
Change-Id: I6cb08b7c56e5e6fc160fb5abc86d68e04a01f8de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2881917
Auto-Submit: Nico Weber <thakis@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@google.com>
Reviewed-by: Dirk Pranke <dpranke@google.com>

download_from_google_storage.py

@@ -76,7 +76,8 @@ class Gsutil(object):
   MAX_TRIES = 5
   RETRY_BASE_DELAY = 5.0
   RETRY_DELAY_MULTIPLE = 1.3
-  VPYTHON = 'vpython.bat' if GetNormalizedPlatform() == 'win32' else 'vpython'
+  VPYTHON3 = ('vpython3.bat'
+              if GetNormalizedPlatform() == 'win32' else 'vpython3')
 
   def __init__(self, path, boto_path=None, version='4.28'):
     if not os.path.exists(path):
@@ -100,12 +101,12 @@ class Gsutil(object):
     return env
 
   def call(self, *args):
-    cmd = [self.VPYTHON, self.path, '--force-version', self.version]
+    cmd = [self.VPYTHON3, self.path, '--force-version', self.version]
     cmd.extend(args)
     return subprocess2.call(cmd, env=self.get_sub_env())
 
   def check_call(self, *args):
-    cmd = [self.VPYTHON, self.path, '--force-version', self.version]
+    cmd = [self.VPYTHON3, self.path, '--force-version', self.version]
     cmd.extend(args)
     ((out, err), code) = subprocess2.communicate(
         cmd,