Bug 1833152 - Make about:third-party wait until module processing is ready before displaying modules r=chutten

This prevents the problem where restarting Firefox with an about:third-party tab active would show that no modules were loaded.

Differential Revision: https://phabricator.services.mozilla.com/D181515

toolkit/components/aboutthirdparty/content/aboutThirdParty.js

@@ -52,6 +52,21 @@ function moduleCompareForDisplay(a, b) {
 async function fetchData() {
   let data = null;
   try {
+    // Wait until the module load events are ready (bug 1833152)
+    const sleep = delayInMs =>
+      new Promise(resolve => setTimeout(resolve, delayInMs));
+    let loadEventsReady = Services.telemetry.areUntrustedModuleLoadEventsReady;
+    let numberOfAttempts = 0;
+    // Just to make sure we don't infinite loop here. (this is normally quite
+    // quick) If we do hit this limit, the page will return an empty list of
+    // modules.
+    const MAX_ATTEMPTS = 30;
+    while (!loadEventsReady && numberOfAttempts < MAX_ATTEMPTS) {
+      await sleep(1000);
+      numberOfAttempts++;
+      loadEventsReady = Services.telemetry.areUntrustedModuleLoadEventsReady;
+    }
+
     data = await Services.telemetry.getUntrustedModuleLoadEvents(
       Services.telemetry.INCLUDE_OLD_LOADEVENTS |
         Services.telemetry.KEEP_LOADEVENTS_NEW |

toolkit/components/telemetry/core/Telemetry.cpp

@@ -663,6 +663,16 @@ TelemetryImpl::GetUntrustedModuleLoadEvents(uint32_t aFlags, JSContext* cx,
 #endif
 }
 
+NS_IMETHODIMP
+TelemetryImpl::GetAreUntrustedModuleLoadEventsReady(bool* ret) {
+#if defined(XP_WIN)
+  *ret = DllServices::Get()->IsReadyForBackgroundProcessing();
+  return NS_OK;
+#else
+  return NS_ERROR_NOT_IMPLEMENTED;
+#endif
+}
+
 #if defined(MOZ_GECKO_PROFILER)
 class GetLoadedModulesResultRunnable final : public Runnable {
   nsMainThreadPtrHandle<Promise> mPromise;

toolkit/components/telemetry/core/nsITelemetry.idl

@@ -240,6 +240,12 @@ interface nsITelemetry : nsISupports
   [implicit_jscontext]
   Promise getUntrustedModuleLoadEvents([optional] in unsigned long aFlags);
 
+  /*
+   * Whether the untrusted module load events are ready for processing.
+   * Calling getUntrustedModuleLoadEvents() before this attribute is true
+   * will result in an empty array. */
+  readonly attribute boolean areUntrustedModuleLoadEventsReady;
+
   /*
    * Asynchronously get an array of the modules loaded in the process.
    *