[M147] Revert^3 "Default enable WebRTC-HeaderExtensionNegotiateMemory"

Original change's description:
> Revert^3 "Default enable WebRTC-HeaderExtensionNegotiateMemory"
> 
> This reverts commit 2f06978.
> 
> Reland "Default enable WebRTC-HeaderExtensionNegotiateMemory"
> 
> This reverts commit 2f06978.
> 
> Reason for revert: Abundance of caution - want more canary time.
> 
> Original change's description:
> > Revert^2 "Default enable WebRTC-HeaderExtensionNegotiateMemory"
> >
> > This reverts commit 74d988f.
> >
> > Reland "Default enable WebRTC-HeaderExtensionNegotiateMemory"
> >
> > This reverts commit 74d988f.
> >
> > Reason for revert: Added code to skip stopped transceivers
> >
> > Original change's description:
> > > Revert "Default enable WebRTC-HeaderExtensionNegotiateMemory"
> > >
> > > This reverts commit 4ecf297.
> > >
> > > Reason for revert: Impacted unexpected application usages
> > >
> > > Original change's description:
> > > > Default enable WebRTC-HeaderExtensionNegotiateMemory
> > > >
> > > > Spec change: w3c/webrtc-extensions#238
> > > >
> > > > Chromestatus entry for change: https://chromestatus.com/feature/5135528638939136
> > > >
> > > > Bug: webrtc:439514253
> > > > Change-Id: I296f2f06dd69b4e30be419b44c926acfd2722e2d
> > > > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/407821
> > > > Commit-Queue: Harald Alvestrand <hta@webrtc.org>
> > > > Reviewed-by: Guido Urdaneta <guidou@webrtc.org>
> > > > Cr-Commit-Position: refs/heads/main@{#45993}
> > >
> > > Bug: webrtc:439514253, chromium:467164231
> > > Change-Id: I95dbc8cbaf1b769ffaea291801684bc26e4b9ccb
> > > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/433102
> > > Reviewed-by: Guido Urdaneta <guidou@webrtc.org>
> > > Commit-Queue: Harald Alvestrand <hta@webrtc.org>
> > > Cr-Commit-Position: refs/heads/main@{#46456}
> >
> > Bug: webrtc:439514253, chromium:467164231
> > Change-Id: I2df85ba25016374a52abb13037cdca74fb1a395d
> > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/453240
> > Reviewed-by: Guido Urdaneta <guidou@webrtc.org>
> > Commit-Queue: Guido Urdaneta <guidou@webrtc.org>
> > Cr-Commit-Position: refs/heads/main@{#47038}
> 
> No-Try: True
> Bug: webrtc:439514253, chromium:467164231, webrtc:489813847
> Change-Id: Id2151293ffe14d2238a1363dd7df679c8a27c42f
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/453820
> Commit-Queue: Harald Alvestrand <hta@webrtc.org>
> Reviewed-by: Guido Urdaneta <guidou@webrtc.org>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Cr-Commit-Position: refs/heads/main@{#47093}

(cherry picked from commit 5f9534d9205a870d40aff649967a38fbde7d7653)

Bug: chromium:491748676,webrtc:439514253,chromium:467164231,webrtc:489813847
Change-Id: Id2151293ffe14d2238a1363dd7df679c8a27c42f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/455980
Auto-Submit: Chrome Cherry Picker <chrome-cherry-picker@chops-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/branch-heads/7727@{#1}
Cr-Branched-From: 5788235-refs/heads/main@{#47086}

Author: Harald Alvestrand

pc/rtp_transceiver.cc

@@ -1224,19 +1224,19 @@ void RtpTransceiver::OnNegotiationUpdate(
   RTC_DCHECK(content);
   if (sdp_type == SdpType::kAnswer || sdp_type == SdpType::kPrAnswer) {
     negotiated_header_extensions_ = content->rtp_header_extensions();
-    if (!env_.field_trials().IsDisabled(
+    if (env_.field_trials().IsEnabled(
             "WebRTC-HeaderExtensionNegotiateMemory")) {
       header_extensions_to_negotiate_ = GetNegotiatedHeaderExtensions();
     }
   } else if (sdp_type == SdpType::kOffer) {
-    if (!env_.field_trials().IsDisabled(
+    if (env_.field_trials().IsEnabled(
             "WebRTC-HeaderExtensionNegotiateMemory")) {
       header_extensions_for_rollback_ = header_extensions_to_negotiate_;
       header_extensions_to_negotiate_ =
           GetOfferedAndImplementedHeaderExtensions(content);
     }
   } else if (sdp_type == SdpType::kRollback) {
-    if (!env_.field_trials().IsDisabled(
+    if (env_.field_trials().IsEnabled(
             "WebRTC-HeaderExtensionNegotiateMemory")) {
       RTC_CHECK(!header_extensions_for_rollback_.empty());
       header_extensions_to_negotiate_ = header_extensions_for_rollback_;

pc/rtp_transmission_manager.cc

@@ -284,8 +284,7 @@ RtpTransmissionManager::CreateAndAddTransceiver(
   RTC_DCHECK(!FindSenderById(sender_id));
   std::vector<RtpHeaderExtensionCapability> header_extensions =
       std::move(header_extensions_to_negotiate);
-  if (!env_.field_trials().IsDisabled(
-          "WebRTC-HeaderExtensionNegotiateMemory")) {
+  if (env_.field_trials().IsEnabled("WebRTC-HeaderExtensionNegotiateMemory")) {
     // If we have already negotiated header extensions for this type,
     // and it is not stopped,
     // reuse the negotiated state for new transceivers of the same type.