Docserver: Update Future.Then() to be more Promise-like

BUG=306341
NOTRY=True

Review URL: https://codereview.chromium.org/417163004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@287482 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 5 insertions, 6 deletions

diff --git a/chrome/common/extensions/docs/server2/file_system.py b/chrome/common/extensions/docs/server2/file_system.py
index 99e33c5..1e5b567 100644
--- a/chrome/common/extensions/docs/server2/file_system.py
+++ b/chrome/common/extensions/docs/server2/file_system.py
@@ -106,13 +106,12 @@ class FileSystem(object):
       return Future(value=True)
 
     parent, base = SplitParent(path)
-    list_future = self.ReadSingle(ToDirectory(parent))
-    def resolve():
-      try:
-        return base in list_future.Get()
-      except FileNotFoundError:
+    def handle(error):
+      if isinstance(error, FileNotFoundError):
         return False
-    return Future(callback=resolve)
+      raise error
+    return self.ReadSingle(ToDirectory(parent)).Then(lambda l: base in l,
+                                                     handle)
 
   def Refresh(self):
     '''Asynchronously refreshes the content of the FileSystem, returning a