Revert "Third try of ResourceLoadViaDataPipe"

This reverts commit 6c2e6729.

Reason for revert: https://bugs.chromium.org/p/chromium/issues/detail?id=929793#c6

Original change's description:
> Third try of ResourceLoadViaDataPipe
> 
> Flipping the flag revealed a couple of issues which were fixed:
> - OnTransferSizeUpdated(): https://crrev.com/c/1454344
> - One more PostTask() made tests more flaky: https://crrev.com/c/1454345
> 
> I hope third try will go well.
> 
> Bug: 894819
> Change-Id: Icc6159622aacd5c4a4c250a0834bf4c3641d916a
> Reviewed-on: https://chromium-review.googlesource.com/c/1454062
> Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
> Commit-Queue: Kinuko Yasuda <kinuko@chromium.org>
> Auto-Submit: Makoto Shimazu <shimazu@chromium.org>
> Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#629089}

TBR=kinuko@chromium.org,shimazu@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 894819
Change-Id: I9aca1329997e4f2517cd72bc79020bf2d147af35
Reviewed-on: https://chromium-review.googlesource.com/c/1459584Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Commit-Queue: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630143}

third_party/blink/common/features.cc

@@ -120,7 +120,7 @@ const base::Feature kRTCOfferExtmapAllowMixed{
 // WebURLLoaderClient::DidStartLoadingResponseBody() instead of
 // WebURLLoaderClient::DidReceiveData().
 const base::Feature kResourceLoadViaDataPipe{"ResourceLoadViaDataPipe",
-                                             base::FEATURE_ENABLED_BY_DEFAULT};
+                                             base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kServiceWorkerImportedScriptUpdateCheck{
     "ServiceWorkerImportedScriptUpdateCheck",