Allow CertNetFetcher to be shutdown from the network thread

net/cert/cert_net_fetcher.h

Index: net/cert/cert_net_fetcher.h
diff --git a/net/cert/cert_net_fetcher.h b/net/cert/cert_net_fetcher.h
index 56a74948117db4f6ae95432dd9a721967a2cc0f3..2a45fe3b6f7407e944ee5b295b2739a7bdf84638 100644
--- a/net/cert/cert_net_fetcher.h
+++ b/net/cert/cert_net_fetcher.h
@@ -20,16 +20,15 @@ class GURL;
 namespace net {
 
 // CertNetFetcher is a synchronous interface for fetching AIA URLs and CRL
-// URLs.
+// URLs. It is shared between a caller thread (which starts and waits for
+// fetches), and a network thread (which does the actual fetches). It can be
+// shutdown from the network thread to cancel outstanding requests.
 //
 // A Request object is returned when starting a fetch. The consumer can
 // use this as a handle for aborting the request (by freeing it), or reading
 // the result of the request (WaitForResult)
-//
-// This interface is expected to be operated from a single thread.
-//
-// The CertNetFetcher must outlive all Request objects it creates.
-class NET_EXPORT CertNetFetcher {
+class NET_EXPORT CertNetFetcher
+    : public base::RefCountedThreadSafe<CertNetFetcher> {
  public:
   class Request {
    public:
@@ -47,7 +46,12 @@ class NET_EXPORT CertNetFetcher {
 
   CertNetFetcher() {}
 
-  virtual ~CertNetFetcher() {}
+  // Shuts down the CertNetFetcher and cancels outstanding network requests. It
+  // is not guaranteed that any outstanding or subsequent
+  // Request::WaitForResult() calls will be completed. Shutdown() must be called
+  // from the network thread. It can be called more than once, but must be
+  // called before the CertNetFetcher is destroyed.
+  virtual void Shutdown() = 0;
 
   // The Fetch*() methods start a request which can be cancelled by
   // deleting the returned Request. Here is the meaning of the common
@@ -76,7 +80,11 @@ class NET_EXPORT CertNetFetcher {
       int timeout_milliseconds,
       int max_response_bytes) = 0;
 
+ protected:
+  virtual ~CertNetFetcher() {}
+
  private:
+  friend class base::RefCountedThreadSafe<CertNetFetcher>;
   DISALLOW_COPY_AND_ASSIGN(CertNetFetcher);
 };