Reland "PM: Enable service worker relationships."

This is a reland of 7fb78e28
The crashes and DCHECKs should be fixed with
https://crrev.com/c/2581939.

Original change's description:
> PM: Enable service worker relationships.
>
> This change is to get some DCHECK crashes on Albatross. It will be
> reverted after it's been on Canary for a day or so.
>
> Bug: 1143281
> Change-Id: I6d125dfbae9699e7292a9aa0336070b005bd03c3
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2571638
> Auto-Submit: Sigurður Ásgeirsson <siggi@chromium.org>
> Reviewed-by: Patrick Monette <pmonette@chromium.org>
> Commit-Queue: Sigurður Ásgeirsson <siggi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#833405}

Bug: 1143281
Change-Id: I52a8332dcd151cd42d6e85f5bbaf4dc094e7d995
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2582726
Commit-Queue: Sigurður Ásgeirsson <siggi@chromium.org>
Commit-Queue: Joe Mason <joenotcharles@chromium.org>
Auto-Submit: Sigurður Ásgeirsson <siggi@chromium.org>
Reviewed-by: Joe Mason <joenotcharles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835338}

components/performance_manager/features.cc

@@ -47,7 +47,7 @@ TabLoadingFrameNavigationThrottlesParams::GetParams() {
 }
 
 const base::Feature kServiceWorkerRelationshipsInGraph{
-    "ServiceWorkerRelationshipsInGraph", base::FEATURE_DISABLED_BY_DEFAULT};
+    "ServiceWorkerRelationshipsInGraph", base::FEATURE_ENABLED_BY_DEFAULT};
 
 }  // namespace features
 }  // namespace performance_manager