Add DeferAllScript to field_trial_testing

Bug: 960961
Change-Id: I9cb66d13461cae042ec5626bd27b7b3633abcd09
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1759231
Auto-Submit: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Doug Arnett <dougarnett@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: Jesse Doherty <jwd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688231}

testing/variations/fieldtrial_testing_config.json

@@ -1833,6 +1833,21 @@
             ]
         }
     ],
+    "DeferAllScript": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "DeferAllScriptPreviews_Enabled_20190814",
+                    "enable_features": [
+                        "DeferAllScript"
+                    ]
+                }
+            ]
+        }
+    ],
     "DialMediaRouteProvider": [
         {
             "platforms": [