Cancel the timeout in SubKeyRequest destructor.

This could avoid a potential crash.

Bug: 741054
Change-Id: I7f606d0edc3741b05b73f678f7a2e28c343852f4
Reviewed-on: https://chromium-review.googlesource.com/567463Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Commit-Queue: Mathieu Perreault <mathp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485934}

components/payments/core/subkey_requester.cc

@@ -45,7 +45,7 @@ class SubKeyRequest : public SubKeyRequester::Request {
         base::TimeDelta::FromSeconds(timeout_seconds));
   }
 
-  ~SubKeyRequest() override {}
+  ~SubKeyRequest() override { on_timeout_.Cancel(); }
 
   void OnRulesLoaded() override {
     on_timeout_.Cancel();