Optimize video_module's __init__ method.

The overall behavior of the __init__ method has remained the same.
What's changed is how it determines whether a field is explicitly set.

Instead of using the slower performing editable_metadata_fields, it
calls _field_data.has directly to check for explicitly set fields.

common/lib/xmodule/xmodule/video_module/video_module.py

@@ -304,14 +304,7 @@ class VideoDescriptor(VideoFields, VideoTranscriptsMixin, VideoStudioViewHandler
             self._field_data.set_many(self, field_data)
             del self.data
 
-        editable_fields = super(VideoDescriptor, self).editable_metadata_fields
-
         self.source_visible = False
-        # Set download_video field to default value if its not explicitly set for backward compatibility.
-        download_video = editable_fields['download_video']
-        if not download_video['explicitly_set']:
-            self.download_video = self.download_video
-
         if self.source:
             # If `source` field value exist in the `html5_sources` field values,
             # then delete `source` field value and use value from `html5_sources` field.
@@ -320,14 +313,17 @@ class VideoDescriptor(VideoFields, VideoTranscriptsMixin, VideoStudioViewHandler
                 self.download_video = True
             else:  # Otherwise, `source` field value will be used.
                 self.source_visible = True
-                if not download_video['explicitly_set']:
+                if not self.fields['download_video'].is_set_on(self):
                     self.download_video = True
 
+        # Set download_video field to default value if its not explicitly set for backward compatibility.
+        if not self.fields['download_video'].is_set_on(self):
+            self.download_video = self.download_video
+
         # for backward compatibility.
         # If course was existed and was not re-imported by the moment of adding `download_track` field,
         # we should enable `download_track` if following is true:
-        download_track = editable_fields['download_track']
-        if not download_track['explicitly_set'] and self.track:
+        if not self.fields['download_track'].is_set_on(self) and self.track:
             self.download_track = True
 
     def editor_saved(self, user, old_metadata, old_content):

lms/djangoapps/courseware/tests/test_video_mongo.py

 # -*- coding: utf-8 -*-
 """Video xmodule tests in mongo."""
 import json
-import unittest
 from collections import OrderedDict
-from mock import patch, PropertyMock, MagicMock
+from mock import patch, MagicMock
 
 from django.conf import settings
 
-from xblock.fields import ScopeIds
-from xblock.field_data import DictFieldData
-
-from xmodule.video_module import create_youtube_string, VideoDescriptor
+from xmodule.video_module import create_youtube_string
 from xmodule.x_module import STUDENT_VIEW
-from xmodule.tests import get_test_descriptor_system
 from xmodule.tests.test_video import VideoDescriptorTestBase
 
-from edxval.api import (
-    ValVideoNotFoundError,
-    get_video_info,
-    create_profile,
-    create_video
-)
-import mock
+from edxval.api import create_profile, create_video
 
 from . import BaseTestXmodule
 from .test_video_xml import SOURCE_XML
@@ -417,7 +406,7 @@ class TestGetHtmlMethod(BaseTestXmodule):
         # it'll just fall back to the values in the VideoDescriptor.
         self.assertIn("example_source.mp4", self.item_descriptor.render(STUDENT_VIEW).content)
 
-    @mock.patch('edxval.api.get_video_info')
+    @patch('edxval.api.get_video_info')
     def test_get_html_with_mocked_edx_video_id(self, mock_get_video_info):
         mock_get_video_info.return_value = {
             'url': '/edxval/video/example',
@@ -798,77 +787,18 @@ class TestVideoDescriptorInitialization(BaseTestXmodule):
         self.assertFalse(self.item_descriptor.source_visible)
 
     def test_download_video_is_explicitly_set(self):
-        with patch(
-            'xmodule.editing_module.TabsEditingDescriptor.editable_metadata_fields',
-            new_callable=PropertyMock,
-            return_value={
-                'download_video': {
-                    'default_value': False,
-                    'explicitly_set': True,
-                    'display_name': 'Video Download Allowed',
-                    'help': 'Show a link beneath the video to allow students to download the video.',
-                    'type': 'Boolean',
-                    'value': False,
-                    'field_name': 'download_video',
-                    'options': [
-                        {'display_name': "True", "value": True},
-                        {'display_name': "False", "value": False}
-                    ],
-                },
-                'html5_sources': {
-                    'default_value': [],
-                    'explicitly_set': False,
-                    'display_name': 'Video Sources',
-                    'help': 'A list of filenames to be used with HTML5 video.',
-                    'type': 'List',
-                    'value': [u'http://youtu.be/3_yD_cEKoCk.mp4'],
-                    'field_name': 'html5_sources',
-                    'options': [],
-                },
-                'source': {
-                    'default_value': '',
-                    'explicitly_set': False,
-                    'display_name': 'Download Video',
-                    'help': 'The external URL to download the video.',
-                    'type': 'Generic',
-                    'value': u'http://example.org/video.mp4',
-                    'field_name': 'source',
-                    'options': [],
-                },
-                'track': {
-                    'default_value': '',
-                    'explicitly_set': False,
-                    'display_name': 'Download Transcript',
-                    'help': 'The external URL to download the timed transcript track.',
-                    'type': 'Generic',
-                    'value': u'http://some_track.srt',
-                    'field_name': 'track',
-                    'options': [],
-                },
-                'download_track': {
-                    'default_value': False,
-                    'explicitly_set': False,
-                    'display_name': 'Transcript Download Allowed',
-                    'help': 'Show a link beneath the video to allow students to download the transcript. Note: You must add a link to the HTML5 Transcript field above.',
-                    'type': 'Generic',
-                    'value': False,
-                    'field_name': 'download_track',
-                    'options': [],
-                },
-                'transcripts': {},
-                'handout': {},
-            }
-        ):
         metadata = {
             'track': u'http://some_track.srt',
             'source': 'http://example.org/video.mp4',
             'html5_sources': ['http://youtu.be/3_yD_cEKoCk.mp4'],
+            'download_video': False,
         }
 
         self.initialize_module(metadata=metadata)
 
         fields = self.item_descriptor.editable_metadata_fields
         self.assertIn('source', fields)
+        self.assertIn('download_video', fields)
 
         self.assertFalse(self.item_descriptor.download_video)
         self.assertTrue(self.item_descriptor.source_visible)