Revert "AppCache: Enable correct 304 handling by default."

This reverts commit 93682cb5.

Reason for revert: The feature crashes on Windows -- https://crbug.com/1052041

Original change's description:
> AppCache: Enable correct 304 handling by default.
> 
> We'll monitor the fix as it goes through the Chrome release waterfall,
> instead of doing a Finch-based trial. This frees us from having to
> reason about enterprises that may disable Finch.
> 
> Bug: 989611
> Change-Id: I50389c12d31f63fa6257d879f3d840ffde2cb27e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2052245
> Commit-Queue: Victor Costan <pwnall@chromium.org>
> Commit-Queue: Chase Phillips <cmp@chromium.org>
> Auto-Submit: Victor Costan <pwnall@chromium.org>
> Reviewed-by: Chase Phillips <cmp@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#740894}

TBR=cmp@chromium.org,pwnall@chromium.org

Change-Id: Ieeb9be42038ba56e176b0ba6a7ab0c84629fea1c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 989611
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2055007Reviewed-by: Victor Costan <pwnall@chromium.org>
Commit-Queue: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741154}

content/browser/appcache/appcache_update_job.cc

@@ -211,7 +211,7 @@ const base::Feature kAppCacheManifestScopeChecksFeature{
     "AppCacheManifestScopeChecks", base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kAppCacheUpdateResourceOn304Feature{
-    "AppCacheUpdateResourceOn304", base::FEATURE_ENABLED_BY_DEFAULT};
+    "AppCacheUpdateResourceOn304", base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Helper class for collecting hosts per frontend when sending notifications
 // so that only one notification is sent for all hosts using the same frontend.