Fix crash in OfflinePageAutoFetcher

Previously, it was possible that the RenderFrameHost was destroyed before
attempted access by OfflinePageAutoFetcher::Create().

The fix is to avoid passing a task runner, which would PostTask().

Bug: 1000002
Change-Id: Ibb3859e9a859442cd80ef04d483c5c4ea37d01f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1782695Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Dan H <harringtond@chromium.org>
Cr-Commit-Position: refs/heads/master@{#693827}

chrome/browser/chrome_content_browser_client.cc

@@ -4429,8 +4429,7 @@ void ChromeContentBrowserClient::InitWebContextInterfaces() {
 
 #if defined(OS_ANDROID)
   frame_interfaces_parameterized_->AddInterface(
-      base::BindRepeating(&offline_pages::OfflinePageAutoFetcher::Create),
-      base::CreateSingleThreadTaskRunner({BrowserThread::UI}));
+      base::BindRepeating(&offline_pages::OfflinePageAutoFetcher::Create));
 #endif
 }