add testing config for DownloadWithServicification

BUG=695115

Change-Id: I58d7e2ddbc004be6fcf16ca2b203e0f85132645f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1911223
Commit-Queue: Min Qin <qinmin@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714716}

testing/variations/fieldtrial_testing_config.json

@@ -2104,6 +2104,21 @@
             ]
         }
     ],
+    "DownloadWithServicificationM77": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "ServiceManagerForDownload"
+                    ]
+                }
+            ]
+        }
+    ],
     "DownloadsAutoResumptionNative": [
         {
             "platforms": [