Fix two URLRequestJob subclasses that didn't support cancellation

components/about_handler/url_request_about_job.cc

Index: components/about_handler/url_request_about_job.cc
diff --git a/components/about_handler/url_request_about_job.cc b/components/about_handler/url_request_about_job.cc
index 880685a1b8d3654deaeab8070a91da22948033ab..71e7c1eafc57c7f9448e6c3d43e6ac0014f08de4 100644
--- a/components/about_handler/url_request_about_job.cc
+++ b/components/about_handler/url_request_about_job.cc
@@ -30,6 +30,11 @@ void URLRequestAboutJob::Start() {
       base::Bind(&URLRequestAboutJob::StartAsync, weak_factory_.GetWeakPtr()));
 }
 
+void URLRequestAboutJob::Kill() {
+  weak_factory_.InvalidateWeakPtrs();
+  URLRequestJob::Kill();
+}
+
 bool URLRequestAboutJob::GetMimeType(std::string* mime_type) const {
   *mime_type = "text/html";
   return true;