Runtime::RunMicrotask should silent return if no pending microtask work (rather than asserting)

src/runtime.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 14667 matching lines @@
   CONVERT_BOOLEAN_ARG_CHECKED(new_state, 0);
   bool old_state = isolate->microtask_pending();
   isolate->set_microtask_pending(new_state);
   return isolate->heap()->ToBoolean(old_state);
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_RunMicrotasks) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 0);
-  Execution::RunMicrotasks(isolate);
+  if (isolate->microtask_pending())
+    Execution::RunMicrotasks(isolate);
   return isolate->heap()->undefined_value();
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_GetMicrotaskState) {
   SealHandleScope shs(isolate);
   ASSERT(args.length() == 0);
   return isolate->heap()->microtask_state();
 }
 
@@ skipping 266 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal