Let the second pass phantom callbacks run in a separate task on the foreground thread.

test/unittests/test-utils.cc

Index: test/unittests/test-utils.cc
diff --git a/test/unittests/test-utils.cc b/test/unittests/test-utils.cc
index 522ee1293046cdb50863a498cff6fcf2fb27a846..93a46ed15d50c70221746293251953f2979066b1 100644
--- a/test/unittests/test-utils.cc
+++ b/test/unittests/test-utils.cc
@@ -4,10 +4,12 @@
 
 #include "test/unittests/test-utils.h"
 
+#include "include/libplatform/libplatform.h"
 #include "src/base/platform/time.h"
 #include "src/debug.h"
 #include "src/flags.h"
 #include "src/isolate.h"
+#include "src/v8.h"
 
 namespace v8 {
 
@@ -51,6 +53,9 @@ void TestWithIsolate::SetUpTestCase() {
 // static
 void TestWithIsolate::TearDownTestCase() {
   ASSERT_TRUE(isolate_ != NULL);
+  v8::Platform* platform = internal::V8::GetCurrentPlatform();
+  ASSERT_TRUE(platform != NULL);
+  while (platform::PumpMessageLoop(platform, isolate_)) continue;
   isolate_->Dispose();
   isolate_ = NULL;
   delete array_buffer_allocator_;