Use correct origin as a request initiator.

SearchEngineTabHelper::PageHasOpenSearchDescriptionDocument makes
network requests on behalf of the main frame (using the URLLoaderFactory
created via main frame's RFHI::CreateNetworkServiceDefaultFactory).

Before this CL, the |initiator| argument of ScheduleDownload method
would be incorrectly set based on WebContents::GetURL method.  This was
incorrect because:
- WebContents::GetURL returns the "visible", rather than "committed" URL
- iframe sandbox attribute is ignored (see
  //docs/security/origin-vs-url.md for more details)

This CL fixes this by changing:
  url::Origin::Create(web_contents->GetURL())
into
  frame->GetLastCommittedOrigin()

Bug: 237908
Change-Id: I8d7eef091aeaf26c7f6c65a03009cdf9713d5346
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1913969Reviewed-by: Nasko Oskov <nasko@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715732}

chrome/browser/ui/search_engines/search_engine_tab_helper.cc

@@ -146,7 +146,7 @@ void SearchEngineTabHelper::PageHasOpenSearchDescriptionDocument(
   // new keyword will be created when done.
   TemplateURLFetcherFactory::GetForProfile(profile)->ScheduleDownload(
       keyword, osdd_url, entry->GetFavicon().url,
-      url::Origin::Create(web_contents()->GetURL()), url_loader_factory.get(),
+      frame->GetLastCommittedOrigin(), url_loader_factory.get(),
       frame->GetRoutingID(),
       static_cast<int>(content::ResourceType::kSubResource));
 }