Reland "EDK: Move //mojo/edk/system/waitable_event* to edk/util."

mojo/edk/system/master_connection_manager.h

Index: mojo/edk/system/master_connection_manager.h
diff --git a/mojo/edk/system/master_connection_manager.h b/mojo/edk/system/master_connection_manager.h
index e751e4decf9851573eed2eb261c2b7ba8f2f1ae6..09a9fee521121cc23c7f604a9189c54f83095514 100644
--- a/mojo/edk/system/master_connection_manager.h
+++ b/mojo/edk/system/master_connection_manager.h
@@ -28,9 +28,11 @@ class MasterProcessDelegate;
 using SlaveInfo = void*;
 }
 
-namespace system {
-
+namespace util {
 class AutoResetWaitableEvent;
+}
+
+namespace system {
 
 // The |ConnectionManager| implementation for the master process.
 //
@@ -116,7 +118,7 @@ class MasterConnectionManager final : public ConnectionManager {
   void AddSlaveOnPrivateThread(embedder::SlaveInfo slave_info,
                                embedder::ScopedPlatformHandle platform_handle,
                                ProcessIdentifier slave_process_identifier,
-                               AutoResetWaitableEvent* event);
+                               util::AutoResetWaitableEvent* event);
   // Called by |Helper::OnError()|.
   void OnError(ProcessIdentifier process_identifier);
   // Posts a call to |master_process_delegate_->OnSlaveDisconnect()|.