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..1b30c0b9ec7af187bb8a39f3d7b7946ea47f9b33 100644
--- a/net/dns/host_resolver.h
+++ b/net/dns/host_resolver.h
@@ -42,6 +42,20 @@ 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. |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.

[mmenke, 2016/07/19 19:03:55]

This comment is outdated (There is no |req| or specified request,
ChangeRequestPriority can't be called after the request was cancelled, since the
way to cancel the request is now bug deleting it)

[maksims (do not use this acc), 2016/07/21 07:12:45]

Done.

+    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 +129,6 @@ 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 +154,26 @@ 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
+  // |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. When Resolve() is called, the request
+  // is filled with a request handle and attached to a job. After the request
+  // has completed, [out_req] is detached from the job.

[mmenke, 2016/07/19 19:03:55]

job is an internal implementation detail of the HostResolverImpl, so shouldn't
be mentioned in the HostResolver docs.  I think this paragraph can be combined
with the previous one, and say something like:

"|out_req| must be non-NULL. If the request is not completed synchronously, it
will be filled with a handle to the request. It must be completed or destroyed
before the HostResolver itself is destroyed."

[maksims (do not use this acc), 2016/07/21 07:12:45]

Requests can even be cancelled after the HostResolver itself is destroyed. There
are no restrictions for that. 

+  //
+  // Requests can be cancelled any time during a resolve job by deletion of the
+  // [out_req]. If it is deleted before Resolve() has completed it's job, the
+  // request will not be completed.

[mmenke, 2016/07/19 19:03:55]

Maybe delete "during a resolve job", and remove the second sentence?  Or maybe
replace with paragraph with something like "Deleting |out_req| will cancel the
request, and cause |callback| not to be invoked."

[maksims (do not use this acc), 2016/07/21 07:12:45]

Done.

+  //
   // 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