Make ResumableUploadError derive from HttpError.

Fixes issue #242.

Reviewed in https://codereview.appspot.com/7415048/.

apiclient/errors.py

@@ -93,7 +93,7 @@ class MediaUploadSizeError(Error):
   pass
 
 
-class ResumableUploadError(Error):
+class ResumableUploadError(HttpError):
   """Error occured during resumable upload."""
   pass
 

apiclient/http.py

@@ -744,7 +744,7 @@ class HttpRequest(object):
       if resp.status == 200 and 'location' in resp:
         self.resumable_uri = resp['location']
       else:
-        raise ResumableUploadError("Failed to retrieve starting URI.")
+        raise ResumableUploadError(resp, content)
     elif self._in_error_state:
       # If we are in an error state then query the server for current state of
       # the upload by sending an empty PUT and reading the 'range' header in

tests/test_discovery.py

@@ -769,7 +769,11 @@ class Discovery(unittest.TestCase):
         'location': 'http://upload.example.com'}, ''),
       ])
 
-    self.assertRaises(ResumableUploadError, request.execute, http=http)
+    try:
+      request.execute(http=http)
+      self.fail('Should have raised ResumableUploadError.')
+    except ResumableUploadError, e:
+      self.assertEqual(400, e.resp.status)
 
   def test_resumable_media_fail_unknown_response_code_subsequent_request(self):
     """Not a multipart upload."""