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

net/dns/mock_host_resolver.h

Index: net/dns/mock_host_resolver.h
diff --git a/net/dns/mock_host_resolver.h b/net/dns/mock_host_resolver.h
index c4312fb21512f5c59d48862978f83e5736812a76..c118125b2fecac500557cb6c01bec0d29e5d56af 100644
--- a/net/dns/mock_host_resolver.h
+++ b/net/dns/mock_host_resolver.h
@@ -82,12 +82,11 @@ class MockHostResolverBase : public HostResolver,
               RequestPriority priority,
               AddressList* addresses,
               const CompletionCallback& callback,
-              RequestHandle* out_req,
+              std::unique_ptr<Request>* out_req,
               const BoundNetLog& net_log) override;
   int ResolveFromCache(const RequestInfo& info,
                        AddressList* addresses,
                        const BoundNetLog& net_log) override;
-  void CancelRequest(RequestHandle req) override;
   HostCache* GetHostCache() override;
 
   // Resolves all pending requests. It is only valid to invoke this if
@@ -115,12 +114,15 @@ class MockHostResolverBase : public HostResolver,
     return last_request_priority_;
   }
 
+  // Removes a request from |RequestMap|
+  void RemoveRequest(size_t id);
+
  protected:
   explicit MockHostResolverBase(bool use_caching);
 
  private:
-  struct Request;
-  typedef std::map<size_t, Request*> RequestMap;
+  class RequestImpl;
+  typedef std::map<size_t, RequestImpl*> RequestMap;
 
   // Resolve as IP or from |cache_| return cached error or
   // DNS_CACHE_MISS if failed.
@@ -239,12 +241,11 @@ class HangingHostResolver : public HostResolver {
               RequestPriority priority,
               AddressList* addresses,
               const CompletionCallback& callback,
-              RequestHandle* out_req,
+              std::unique_ptr<Request>* out_req,
               const BoundNetLog& net_log) override;
   int ResolveFromCache(const RequestInfo& info,
                        AddressList* addresses,
                        const BoundNetLog& net_log) override;
-  void CancelRequest(RequestHandle req) override {}
 };
 
 // This class sets the default HostResolverProc for a particular scope.  The