Add CanAccessToolchainBucket() to ways to use GStorage.

This allows Googlers who didn't pass existing checks to use G storage and
the Pro version of Visual studio.

BUG=
TBR=maruel

Review URL: https://codereview.chromium.org/382373002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@283250 0039d316-1c4b-4281-b951-d872f2087c98

win_toolchain/get_toolchain_if_necessary.py

@@ -224,7 +224,9 @@ def main():
   current_hash = CalculateHash(target_dir)
   if current_hash not in desired_hashes:
     should_use_gs = False
-    if HaveSrcInternalAccess() or LooksLikeGoogler():
+    if (HaveSrcInternalAccess() or 
+        LooksLikeGoogler() or 
+        CanAccessToolchainBucket()):
       should_use_gs = True
       if not CanAccessToolchainBucket():
         RequestGsAuthentication()