Fix crash when AppBannerClient is null when resolveBeforeInstallPromptPromise is called.

components/test_runner/test_runner.cc

Index: components/test_runner/test_runner.cc
diff --git a/components/test_runner/test_runner.cc b/components/test_runner/test_runner.cc
index 9f79dbbd68279633999e4604991fb9e4855d8bec..ae1fb6b6cbe8be3af9109033b8afb051d756202d 100644
--- a/components/test_runner/test_runner.cc
+++ b/components/test_runner/test_runner.cc
@@ -2958,6 +2958,8 @@ void TestRunner::DispatchBeforeInstallPromptEvent(
 void TestRunner::ResolveBeforeInstallPromptPromise(
     int request_id,
     const std::string& platform) {
+  if (!test_interfaces_->GetAppBannerClient())
+    return;
   test_interfaces_->GetAppBannerClient()->ResolvePromise(request_id, platform);
 }