[unified-heap] Fix test runner

Some tests rely on properly collecting objects on tear down. E.g. mock
objects are expected to die after a test finishes.

Bug: 843903
Change-Id: Ica1daee98be3625e4f2202fe0a73b290b5130ce9
Reviewed-on: https://chromium-review.googlesource.com/c/1293489Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601544}

third_party/blink/renderer/controller/tests/run_all_tests.cc

@@ -55,7 +55,9 @@ int runHelper(base::TestSuite* testSuite) {
   // Collect garbage (including threadspecific persistent handles) in order
   // to release mock objects referred from v8 or Oilpan heap. Otherwise false
   // mock leaks will be reported.
-  blink::V8GCController::CollectAllGarbageForTesting(v8::Isolate::GetCurrent());
+  blink::V8GCController::CollectAllGarbageForTesting(
+      v8::Isolate::GetCurrent(),
+      v8::EmbedderHeapTracer::EmbedderStackState::kEmpty);
 
   content::TearDownBlinkTestEnvironment();