Revert of Delete SignalThread class.

webrtc/rtc_base/nethelpers.h

Index: webrtc/rtc_base/nethelpers.h
diff --git a/webrtc/rtc_base/nethelpers.h b/webrtc/rtc_base/nethelpers.h
index b5f0c01a5cc46fd2766e279c3f5ff6ea9c8c2489..d25879e78599820840063e1df77205717b03d253 100644
--- a/webrtc/rtc_base/nethelpers.h
+++ b/webrtc/rtc_base/nethelpers.h
@@ -19,25 +19,19 @@
 #endif
 
 #include <list>
-#include <memory>
 
 #include "webrtc/rtc_base/asyncresolverinterface.h"
-#include "webrtc/rtc_base/refcount.h"
-#include "webrtc/rtc_base/scoped_ref_ptr.h"
+#include "webrtc/rtc_base/signalthread.h"
 #include "webrtc/rtc_base/sigslot.h"
 #include "webrtc/rtc_base/socketaddress.h"
-#include "webrtc/rtc_base/thread_checker.h"
 
 namespace rtc {
 
-class Thread;
-class TaskQueue;
+class AsyncResolverTest;
 
-// AsyncResolver will perform async DNS resolution, signaling the result on the
-// SignalDone from AsyncResolverInterface when the operation completes.
-// SignalDone is fired on the same thread on which the AsyncResolver was
-// constructed.
-class AsyncResolver : public AsyncResolverInterface {
+// AsyncResolver will perform async DNS resolution, signaling the result on
+// the SignalDone from AsyncResolverInterface when the operation completes.
+class AsyncResolver : public SignalThread, public AsyncResolverInterface {
  public:
   AsyncResolver();
   ~AsyncResolver() override;
@@ -48,34 +42,16 @@ class AsyncResolver : public AsyncResolverInterface {
   void Destroy(bool wait) override;
 
   const std::vector<IPAddress>& addresses() const { return addresses_; }
+  void set_error(int error) { error_ = error; }
 
- private:
-  void ResolveDone(int error, std::vector<IPAddress> addresses);
-
-  class Trampoline : public RefCountInterface {
-   public:
-    Trampoline(AsyncResolver* resolver) : resolver(resolver) {}
-    // Points back to the resolver, as long as it is alive. Cleared
-    // by the AsyncResolver destructor.
-    AsyncResolver* resolver;
-  };
+ protected:
+  void DoWork() override;
+  void OnWorkDone() override;
 
-  // |state_| is non-null while resolution is pending, i.e., set
-  // non-null by Start() and cleared by ResolveDone(). The destructor
-  // clears state_->resolver (assuming |state_| is non-null), to
-  // indicate that the resolver can no longer be accessed.
-  scoped_refptr<Trampoline> state_ ACCESS_ON(construction_thread_);
-
-  Thread* const construction_thread_;
-  // Set to true when Destroy() can't delete the object immediately.
-  // Indicate that the ResolveDone method is now responsible for
-  // deletion. method should delete the object.
-  bool destroyed_ = false;
-  // Queue used only for a single task.
-  std::unique_ptr<TaskQueue> resolver_queue_;
+ private:
   SocketAddress addr_;
   std::vector<IPAddress> addresses_;
-  int error_ = -1;
+  int error_;
 };
 
 // rtc namespaced wrappers for inet_ntop and inet_pton so we can avoid