Launch disallowFetchForDocWrittenScriptsInMainFrameOnSlowConnections

We forgot to launch this by default, and the experiment ended in M63.
Launch now and optionally ramp up M65+.

Bug: 599875
Change-Id: I0e49ec389ab4aa679bd3e98e3493facef04e02b5
Reviewed-on: https://chromium-review.googlesource.com/973559Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Reviewed-by: Nate Chapin <japhet@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544814}

testing/variations/fieldtrial_testing_config.json

@@ -1154,26 +1154,6 @@
             ]
         }
     ],
-    "DisallowFetchForDocWrittenScriptsInMainFrame": [
-        {
-            "platforms": [
-                "android",
-                "chromeos",
-                "linux",
-                "mac",
-                "win"
-            ],
-            "experiments": [
-                {
-                    "name": "DocumentWriteScriptBlockGroup_20161208_Launch",
-                    "params": {
-                        "disallowFetchForDocWrittenScriptsInMainFrame": "false",
-                        "disallowFetchForDocWrittenScriptsInMainFrameOnSlowConnections": "true"
-                    }
-                }
-            ]
-        }
-    ],
     "DownloadHomeMoreButton": [
         {
             "platforms": [

third_party/WebKit/Source/core/frame/Settings.json5

@@ -814,7 +814,7 @@
     // frame inserted via document.write, for users on slow connections.
     {
       name: "disallowFetchForDocWrittenScriptsInMainFrameOnSlowConnections",
-      initial: false,
+      initial: true,
     },
 
     // Whether to disallow network fetches for parser blocking scripts in the main