Join embeder threads on Windows.

runtime/bin/eventhandler_win.h

Index: runtime/bin/eventhandler_win.h
diff --git a/runtime/bin/eventhandler_win.h b/runtime/bin/eventhandler_win.h
index bfd02f945a33bc18c6ec889b774c45a5e00ea1f7..6fe56d95911ff6cae87b0034aea8e320ff68cf28 100644
--- a/runtime/bin/eventhandler_win.h
+++ b/runtime/bin/eventhandler_win.h
@@ -275,7 +275,17 @@ class Handle : public DescriptorInfoBase {
 
   DWORD last_error_;
 
+  ThreadId read_thread_id_;
+  bool read_thread_running_;
+  bool read_thread_finished_;
+  Monitor* read_thread_monitor_;
+
  private:
+  void WaitForReadThreadStarted();
+  void NotifyReadThreadStarted();
+  void WaitForReadThreadFinished();
+  void NotifyReadThreadFinished();
+
   int flags_;
   CRITICAL_SECTION cs_;  // Critical section protecting this object.
 };
@@ -297,6 +307,7 @@ class StdHandle : public FileHandle {
  public:
   explicit StdHandle(HANDLE handle)
       : FileHandle(handle),
+        thread_id_(Thread::kInvalidThreadId),
         thread_wrote_(0),
         write_thread_exists_(false),
         write_thread_running_(false),
@@ -315,6 +326,7 @@ class StdHandle : public FileHandle {
   void RunWriteLoop();
 
  private:
+  ThreadId thread_id_;
   intptr_t thread_wrote_;
   bool write_thread_exists_;
   bool write_thread_running_;
@@ -526,6 +538,9 @@ class EventHandlerImplementation {
  private:
   ClientSocket* client_sockets_head_;
 
+  Monitor* startup_monitor_;
+  ThreadId handler_thread_id_;
+
   TimeoutQueue timeout_queue_;  // Time for next timeout.
   bool shutdown_;
   HANDLE completion_port_;