[d8][predictable] Fix task execution loop

The predictable platform only executed background tasks if at least one
foreground task was executed. Async compilation in Wasm only spawns a
background task though, so that one could be missed.

This CL fixes the loop to also execute background tasks if no foreground
task was executed.

R=ahaas@chromium.org

Bug: v8:11848
Change-Id: Ia0b32427c24a79d5710c784b98528bf431471528
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2944833Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75007}

src/d8/d8.cc

@@ -4531,19 +4531,22 @@ bool ProcessMessages(
     i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
     i::SaveAndSwitchContext saved_context(i_isolate, i::Context());
     SealHandleScope shs(isolate);
-    while (v8::platform::PumpMessageLoop(g_default_platform, isolate,
-                                         behavior())) {
-      MicrotasksScope::PerformCheckpoint(isolate);
-
+    for (bool ran_tasks = true; ran_tasks;) {
+      // Execute one foreground task (if one exists), then microtasks.
+      ran_tasks = v8::platform::PumpMessageLoop(g_default_platform, isolate,
+                                                behavior());
+      if (ran_tasks) MicrotasksScope::PerformCheckpoint(isolate);
+
+      // In predictable mode we push all background tasks into the foreground
+      // task queue of the {kProcessGlobalPredictablePlatformWorkerTaskQueue}
+      // isolate. We execute all background tasks after running one foreground
+      // task.
       if (i::FLAG_verify_predictable) {
-        // In predictable mode we push all background tasks into the foreground
-        // task queue of the {kProcessGlobalPredictablePlatformWorkerTaskQueue}
-        // isolate. We execute the tasks after one foreground task has been
-        // executed.
         while (v8::platform::PumpMessageLoop(
             g_default_platform,
             kProcessGlobalPredictablePlatformWorkerTaskQueue,
             platform::MessageLoopBehavior::kDoNotWait)) {
+          ran_tasks = true;
         }
       }
     }
@@ -4552,13 +4555,9 @@ bool ProcessMessages(
                                  50.0 / base::Time::kMillisecondsPerSecond);
     }
     bool ran_set_timeout = false;
-    if (!RunSetTimeoutCallback(isolate, &ran_set_timeout)) {
-      return false;
-    }
-
+    if (!RunSetTimeoutCallback(isolate, &ran_set_timeout)) return false;
     if (!ran_set_timeout) return true;
   }
-  return true;
 }
 }  // anonymous namespace