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 2d34f2df1f220c6d56a7fc9589f2284e63c9321b..99d0602943bab800162748228888b46aad856daf 100644
--- a/webrtc/rtc_base/nethelpers.h
+++ b/webrtc/rtc_base/nethelpers.h
@@ -19,19 +19,25 @@
 #endif
 
 #include <list>
+#include <memory>
 
 #include "webrtc/base/asyncresolverinterface.h"
-#include "webrtc/base/signalthread.h"
+#include "webrtc/base/refcount.h"
+#include "webrtc/base/scoped_ref_ptr.h"
 #include "webrtc/base/sigslot.h"
 #include "webrtc/base/socketaddress.h"
+#include "webrtc/base/thread_checker.h"
 
 namespace rtc {
 
-class AsyncResolverTest;
+class Thread;
+class TaskQueue;
 
-// AsyncResolver will perform async DNS resolution, signaling the result on
-// the SignalDone from AsyncResolverInterface when the operation completes.
-class AsyncResolver : public SignalThread, public AsyncResolverInterface {
+// 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 {
  public:
   AsyncResolver();
   ~AsyncResolver() override;
@@ -42,16 +48,34 @@ class AsyncResolver : public SignalThread, public AsyncResolverInterface {
   void Destroy(bool wait) override;
 
   const std::vector<IPAddress>& addresses() const { return addresses_; }
-  void set_error(int error) { error_ = error; }
-
- protected:
-  void DoWork() override;
-  void OnWorkDone() override;
 
  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;
+  };
+
+  // |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_;
   SocketAddress addr_;
   std::vector<IPAddress> addresses_;
-  int error_;
+  int error_ = -1;
 };
 
 // rtc namespaced wrappers for inet_ntop and inet_pton so we can avoid