SW: Ignore setting phase when a register job is already COMPLETE.

Calling StopAllServiceWorkersForOrigin and DeleteForOrigin on a SW
context can result in ServiceWorkerRegisterJob::OnStartWorkerFinished
for a job that is already in COMPLETE phase.

This CL bails out setting phase in this case.

Bug: 1031764
Change-Id: I863320d4dbf8606c52d8e55af017dae05d011d4f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1959525
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#723501}

content/browser/service_worker/service_worker_register_job.cc

@@ -550,6 +550,11 @@ void ServiceWorkerRegisterJob::UpdateAndContinue() {
 
 void ServiceWorkerRegisterJob::OnStartWorkerFinished(
     blink::ServiceWorkerStatusCode status) {
+  // Bail out early if the job has already completed.
+  // See https://crbug.com/1031764 for details.
+  if (phase_ == COMPLETE)
+    return;
+
   BumpLastUpdateCheckTimeIfNeeded();
 
   if (status == blink::ServiceWorkerStatusCode::kOk) {