[103] Revert "Enable same-process, cross-origin iframe throttle by de…

…fault."

This reverts commit de62b18.

Reason for revert: it looks like this is causing a number of issues (eg 1330118, 1331021) 

Original change's description:
> Enable same-process, cross-origin iframe throttle by default.
>
> This CL turns on the throttle by default. This can be easily reverted if
> we see problems.
>
> Bug: 958475
> Change-Id: I145fcd24fb83a8a936c784eab718372b6bf6adbd
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3557789
> Reviewed-by: David Bokan <bokan@chromium.org>
> Commit-Queue: James Maclean <wjmaclean@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#986525}

(cherry picked from commit 38b2c4a)

Bug: 958475, 1330118, 1331021
Change-Id: I0019defdad1a1b1cc0c0146f5f1e7e4185ae5411
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3682223
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Commit-Queue: Ian Vollick <vollick@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1009807}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3686773
Cr-Commit-Position: refs/branch-heads/5060@{#491}
Cr-Branched-From: b83393d-refs/heads/main@{#1002911}

third_party/blink/common/features.cc

@@ -990,7 +990,7 @@ const base::Feature kManagedConfiguration{"ManagedConfiguration",
 // have their rendering throttled on display:none or zero-area.
 const base::Feature kThrottleDisplayNoneAndVisibilityHiddenCrossOriginIframes{
     "ThrottleDisplayNoneAndVisibilityHiddenCrossOriginIframes",
-    base::FEATURE_ENABLED_BY_DEFAULT};
+    base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Kill switch for the Interest Group API, i.e. if disabled, the
 // API exposure will be disabled regardless of the OT config.