Conver APIListDataSource to use Future.Then() rather than Get().

chrome/common/extensions/docs/server2/future.py

Index: chrome/common/extensions/docs/server2/future.py
diff --git a/chrome/common/extensions/docs/server2/future.py b/chrome/common/extensions/docs/server2/future.py
index 51c284235cc7706d4f9c9df0f2740cdf18d409b0..8d6312923e0e0418bf2d34753e1854c1a02e0bd3 100644
--- a/chrome/common/extensions/docs/server2/future.py
+++ b/chrome/common/extensions/docs/server2/future.py
@@ -69,13 +69,31 @@ class Future(object):
     '''Creates and returns a future that runs |callback| on the value of this
     future, or runs optional |error_handler| if resolving this future results in
     an exception.
+
+    If |callback| returns a Future then Then() will resolve to the same value

[Yoyo Zhou, 2014/08/05 21:52:36]

These 2 sentences are confusing next to each other.

[not at google - send to devlin, 2014/08/05 23:00:54]

This is tricky to explain. I had another go.

+    of that Future. Otherwise, Then() will resolve to that value.
+
+    For example,
+
+      def fortytwo():
+        return 42
+      def inc(x):
+        return x + 1
+      def inc_future(x):
+        return Future(value=x + 1)
+
+    fortywho().Then(inc).Get()        ==> 43
+    fortywho().Then(inc_future).Get() ==> 43
     '''
     def then():
+      val = None
       try:
         val = self.Get()
       except Exception as e:
-        return error_handler(e)
-      return callback(val)
+        val = error_handler(e)
+      else:
+        val = callback(val)
+      return val.Get() if isinstance(val, Future) else val
     return Future(callback=then)
 
   def Get(self):