[abc] iView: add support for downloading the latest episode of a show

This allows to download using only the show URL instead of
having to find out the latest episode URL manually.

Test using Aussie Rangers which doesn't have an expiry date and
is quite old so it is unlikely to get a new episode, which would
cause the test to fail. The show and latest video URLs are:

https://iview.abc.net.au/show/aussie-rangers
https://iview.abc.net.au/show/aussie-rangers/series/0/video/IP1502W001S00

youtube_dl/extractor/abc.py

@@ -191,3 +191,38 @@ class ABCIViewIE(InfoExtractor):
             'subtitles': subtitles,
             'is_live': is_live,
         }
+
+
+class ABCIViewShowLatestEpisodeIE(InfoExtractor):
+    IE_NAME = 'abc.net.au:iview:show:latest-episode'
+    _VALID_URL = r'https?://iview\.abc\.net\.au/show/(?P<id>[^/]+)$'
+    _GEO_COUNTRIES = ['AU']
+
+    _TESTS = [{
+        'url': 'https://iview.abc.net.au/show/aussie-rangers',
+        'md5': 'd0ef57fb44165e5947f04b06ad30205f',
+        'info_dict': {
+            'id': 'IP1502W001S00',
+            'ext': 'mp4',
+            'title': 'Episode 1',
+            'series': "Aussie Rangers",
+            'description': 'md5:b2b899da064bdec43c3a291314ade444',
+            'upload_date': '20171204',
+            'uploader_id': 'abc2',
+            'timestamp': 1512354840,
+        },
+        'params': {
+            'skip_download': True,
+        },
+    }]
+
+    def _real_extract(self, url):
+        show_id = self._match_id(url)
+        webpage = self._download_webpage(url, show_id)
+        webpage_data = self._search_regex(
+            r'window\.__INITIAL_STATE__\s*=\s*"(.+)"\s*;',
+            webpage, 'initial state')
+        json_data = unescapeHTML(webpage_data).encode('utf-8').decode('unicode_escape')
+        video_data = self._parse_json(json_data, show_id)
+        url = video_data['page']['pageData']['_embedded']['highlightVideo']['shareUrl']
+        return self.url_result(url)

youtube_dl/extractor/extractors.py

@@ -4,6 +4,7 @@ from __future__ import unicode_literals
 from .abc import (
     ABCIE,
     ABCIViewIE,
+    ABCIViewShowLatestEpisodeIE,
 )
 from .abcnews import (
     AbcNewsIE,