Change HostResolver::Resolve() to take an std::unique_ptr<Request>* rather than a RequestHandle*

net/dns/host_resolver.h

Index: net/dns/host_resolver.h
diff --git a/net/dns/host_resolver.h b/net/dns/host_resolver.h
index 5c371e43ad533e66ed0f366c36f5f17bb73e1bf7..c5494b7a68e63a7d40b221e02b9bddf4cc3f895a 100644
--- a/net/dns/host_resolver.h
+++ b/net/dns/host_resolver.h
@@ -42,6 +42,18 @@ class NetLog;
 // goes out of scope).
 class NET_EXPORT HostResolver {
  public:
+  // HostResolver::Request class is used to cancel the request and change it's
+  // priority. It must be owned by consumer. Deletion cancels the request.
+  class Request {
+   public:
+    virtual ~Request() {}
+
+    // Changes the priority of the specified request. Can be called after
+    // Resolve() is called. Can't be called once the request is cancelled or
+    // completed.
+    virtual void ChangeRequestPriority(RequestPriority priority) = 0;
+  };
+
   // |max_concurrent_resolves| is how many resolve requests will be allowed to
   // run in parallel. Pass HostResolver::kDefaultParallelism to choose a
   // default value.
@@ -115,9 +127,6 @@ class NET_EXPORT HostResolver {
     bool is_my_ip_address_;
   };
 
-  // Opaque type used to cancel a request.
-  typedef void* RequestHandle;
-
   // Set Options.max_concurrent_resolves to this to select a default level
   // of concurrency.
   static const size_t kDefaultParallelism = 0;
@@ -143,30 +152,21 @@ class NET_EXPORT HostResolver {
   // callback.  Otherwise the result code is returned immediately from this
   // call.
   //
-  // If |out_req| is non-NULL, then |*out_req| will be filled with a handle to
-  // the async request. This handle is not valid after the request has
-  // completed.
+  // [out_req] must be owned by a caller. If the request is not completed
+  // synchronously, it will be filled with a handle to the request. It must be
+  // completed before the HostResolver itself is destroyed.
+  //
+  // Requests can be cancelled any time by deletion of the [out_req]. Deleting
+  // |out_req| will cancel the request, and cause |callback| not to be invoked.
   //
   // Profiling information for the request is saved to |net_log| if non-NULL.
   virtual int Resolve(const RequestInfo& info,
                       RequestPriority priority,
                       AddressList* addresses,
                       const CompletionCallback& callback,
-                      RequestHandle* out_req,
+                      std::unique_ptr<Request>* out_req,
                       const BoundNetLog& net_log) = 0;
 
-  // Changes the priority of the specified request. |req| is the handle returned
-  // by Resolve(). ChangeRequestPriority must NOT be called after the request's
-  // completion callback has already run or the request was canceled.
-  virtual void ChangeRequestPriority(RequestHandle req,
-                                     RequestPriority priority);
-
-  // Cancels the specified request. |req| is the handle returned by Resolve().
-  // After a request is canceled, its completion callback will not be called.
-  // CancelRequest must NOT be called after the request's completion callback
-  // has already run or the request was canceled.
-  virtual void CancelRequest(RequestHandle req) = 0;
-
   // Resolves the given hostname (or IP address literal) out of cache or HOSTS
   // file (if enabled) only. This is guaranteed to complete synchronously.
   // This acts like |Resolve()| if the hostname is IP literal, or cached value