[Explore] Save custom url parameters when user save slices (#4578)

* [Explore] Save url parameters when user save slices

* remove print

(cherry picked from commit bd9ecbe)

* add unit test

(cherry picked from commit 0f350ad)

* wrapping all request params into url_params

(cherry picked from commit 17197c1)

tests/utils_tests.py

@@ -14,7 +14,8 @@ import numpy
 
 from superset.utils import (
     base_json_conv, datetime_f, json_int_dttm_ser, json_iso_dttm_ser,
-    JSONEncodedDict, memoized, merge_extra_filters, parse_human_timedelta,
+    JSONEncodedDict, memoized, merge_extra_filters, merge_request_params,
+    parse_human_timedelta,
     SupersetException, validate_json, zlib_compress, zlib_decompress_to_string,
 )
 
@@ -216,6 +217,20 @@ class UtilsTestCase(unittest.TestCase):
         merge_extra_filters(form_data)
         self.assertEquals(form_data, expected)
 
+    def test_merge_request_params(self):
+        form_data = {
+            'since': '2000',
+            'until': 'now',
+        }
+        url_params = {
+            'form_data': form_data,
+            'dashboard_ids': '(1,2,3,4,5)',
+        }
+        merge_request_params(form_data, url_params)
+        self.assertIn('url_params', form_data.keys())
+        self.assertIn('dashboard_ids', form_data['url_params'])
+        self.assertNotIn('form_data', form_data.keys())
+
     def test_datetime_f(self):
         self.assertEquals(
             datetime_f(datetime(1990, 9, 21, 19, 11, 19, 626096)),