luci-py/isolateserver.py: Add archive support when downloading.

client/isolated_format.py

Index: client/isolated_format.py
diff --git a/client/isolated_format.py b/client/isolated_format.py
index a71dbc07a839e76152db65ce5297ca302f8ede62..e60a30cacdc1ce8e78aa2dfec7f91d4daf8ca385 100644
--- a/client/isolated_format.py
+++ b/client/isolated_format.py
@@ -37,6 +37,8 @@ SUPPORTED_ALGOS = {
 # Used for serialization.
 SUPPORTED_ALGOS_REVERSE = dict((v, k) for k, v in SUPPORTED_ALGOS.iteritems())
 
+SUPPORTED_ARCHIVES = ['ar']
+
 
 class IsolatedError(ValueError):
   """Generic failure to load a .isolated file."""
@@ -506,6 +508,10 @@ def load_isolated(content, algo):
           elif subsubkey == 's':
             if not isinstance(subsubvalue, (int, long)):
               raise IsolatedError('Expected int or long, got %r' % subsubvalue)
+          elif subsubkey == 'a':
+            if subsubvalue not in SUPPORTED_ARCHIVES:
+              raise IsolatedError('Expected one of \'%s\', got %r' % (
+                  ', '.join(sorted(SUPPORTED_ARCHIVES)), subsubvalue))
           else:
             raise IsolatedError('Unknown subsubkey %s' % subsubkey)
         if bool('h' in subvalue) == bool('l' in subvalue):