New plugin hooks: extra_css_urls() and extra_js_urls()

Closes #214

tests/fixtures.py

@@ -113,6 +113,19 @@ def prepare_connection(conn):
         "select convert_units(100, 'm', 'ft');"
         return (amount * ureg(from_)).to(to_).to_tuple()[0]
     conn.create_function('convert_units', 3, convert_units)
+
+
+@hookimpl
+def extra_css_urls():
+    return ['https://example.com/app.css']
+
+
+@hookimpl
+def extra_js_urls():
+    return [{
+        'url': 'https://example.com/app.js',
+        'sri': 'SRIHASH',
+    }]
 '''
 
 TABLES = '''

tests/test_html.py

@@ -333,6 +333,19 @@ def test_view_html(app_client):
     assert expected == [[str(td) for td in tr.select('td')] for tr in table.select('tbody tr')]
 
 
+def test_plugin_extra_css_urls(app_client):
+    response = app_client.get('/', gather_request=False)
+    assert b'<link rel="stylesheet" href="https://example.com/app.css">' in response.body
+
+
+def test_plugin_extra_js_urls(app_client):
+    response = app_client.get('/', gather_request=False)
+    assert (
+        b'<script src="https://example.com/app.js" integrity="SRIHASH" crossorigin="anonymous"></script>'
+        in response.body
+    )
+
+
 def test_index_metadata(app_client):
     response = app_client.get('/', gather_request=False)
     assert response.status == 200