Bug 1751678 - Make FetchStart uses StarTime when TAO check fails for PerformanceResourceTiming r=smaug

Given the recent Fetch spec updates, Step 8.1 in
https://fetch.spec.whatwg.org/#finalize-and-report-timing specifies
that start time(StartTime) and post-redirect start time(FetchStart) should
be start time when TAO check fails.

Differential Revision: https://phabricator.services.mozilla.com/D141366

dom/performance/PerformanceResourceTiming.cpp

@@ -41,6 +41,13 @@ PerformanceResourceTiming::PerformanceResourceTiming(
 
 PerformanceResourceTiming::~PerformanceResourceTiming() = default;
 
+DOMHighResTimeStamp PerformanceResourceTiming::FetchStart() const {
+  if (mTimingData->TimingAllowed()) {
+    return mTimingData->FetchStartHighRes(mPerformance);
+  }
+  return StartTime();
+}
+
 DOMHighResTimeStamp PerformanceResourceTiming::StartTime() const {
   // Force the start time to be the earliest of:
   //  - RedirectStart

dom/performance/PerformanceResourceTiming.h

@@ -56,9 +56,7 @@ class PerformanceResourceTiming : public PerformanceEntry {
     return mTimingData->WorkerStartHighRes(mPerformance);
   }
 
-  DOMHighResTimeStamp FetchStart() const {
-    return mTimingData->FetchStartHighRes(mPerformance);
-  }
+  DOMHighResTimeStamp FetchStart() const;
 
   DOMHighResTimeStamp RedirectStart(Maybe<nsIPrincipal*>& aSubjectPrincipal,
                                     bool aEnsureSameOriginAndIgnoreTAO) const {

testing/web-platform/meta/resource-timing/cross-origin-start-end-time-with-redirects.html.ini

@@ -1,4 +0,0 @@
-[cross-origin-start-end-time-with-redirects.html]
-  [Verify that cross-origin resources don't implicitly expose their redirect timings]
-    expected: FAIL
-

testing/web-platform/meta/resource-timing/object-not-found-after-cross-origin-redirect.html.ini

@@ -1,7 +0,0 @@
-[object-not-found-after-cross-origin-redirect.html]
-  expected:
-    if (os == "win") and fission: OK
-    if os == "mac": OK
-    [OK, ERROR]
-  [Verify that cross-origin object resources don't implicitly expose their redirect timings]
-    expected: FAIL