Gracefully handle tests finishing simultanously in 2+ secondary windows.

content/shell/renderer/layout_test/blink_test_runner.cc

Index: content/shell/renderer/layout_test/blink_test_runner.cc
diff --git a/content/shell/renderer/layout_test/blink_test_runner.cc b/content/shell/renderer/layout_test/blink_test_runner.cc
index d9bdf7ef78feee2a9005ee237b5c86aec5ea2f52..22b5710d9c5abbdb8676e1cbd17e1e41986385e4 100644
--- a/content/shell/renderer/layout_test/blink_test_runner.cc
+++ b/content/shell/renderer/layout_test/blink_test_runner.cc
@@ -1032,6 +1032,14 @@ void BlinkTestRunner::OnReset() {
 
 void BlinkTestRunner::OnTestFinishedInSecondaryRenderer() {
   DCHECK(is_main_window_ && render_view()->GetMainRenderFrame());
+
+  // Avoid a situation where TestFinished is called twice, because
+  // of a racey test finish in 2 secondary renderers.
+  test_runner::WebTestInterfaces* interfaces =
+      LayoutTestRenderThreadObserver::GetInstance()->test_interfaces();
+  if (!interfaces->TestIsRunning())
+    return;
+
   TestFinished();
 }