Add VerifyHTMLFetchedFromAppCacheBeforeDelay field trial config

This is a reland of [1], which got reverted in [2] due to a mix
or regressions and progressions on the bots. I'm now re-attempting to
land this with a Finch trial.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1953204
[2] https://chromium-review.googlesource.com/c/chromium/src/+/2023497

Bug: 788757
Change-Id: I5193d6a00dae358c047a87478abfadbccccb2fc2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2560124Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Yoav Weiss <yoavweiss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832299}

testing/variations/fieldtrial_testing_config.json

@@ -7334,6 +7334,26 @@
             ]
         }
     ],
+    "VerifyHTMLFetchedFromAppCacheBeforeDelay": [
+        {
+            "platforms": [
+                "windows",
+                "mac",
+                "chromeos",
+                "linux",
+                "ios",
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "VerifyHTMLFetchedFromAppCacheBeforeDelay"
+                    ]
+                }
+            ]
+        }
+    ],
     "VideoToolboxVp9Decoding": [
         {
             "platforms": [