Use pagehide instead of unload in test.

BrowserInitiatedLoadPostCommitErrorPageIgnoredForFramePendingDeletion
just needs to send a message at unload-time, so pagehide is ok.

Bug: 1488371
Change-Id: Idc0452a3ef3abdabd4080365b0fae6db43ea377c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5064827
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1230471}

content/browser/renderer_host/navigation_controller_impl_browsertest.cc

@@ -17190,10 +17190,10 @@ IN_PROC_BROWSER_TEST_P(
 
   RenderFrameHost* frame = shell()->web_contents()->GetPrimaryMainFrame();
 
-  // Create an unload handler and force the browser process to wait before
+  // Create a pagehide handler and force the browser process to wait before
   // deleting |frame|.
   EXPECT_TRUE(ExecJs(frame, R"(
-             window.onunload=function(e){
+             window.onpagehide=function(e){
                window.domAutomationController.send('done');
              };)"));