Revert Mojo-based SyncChannel waiting again

ipc/ipc_sync_message.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef IPC_IPC_SYNC_MESSAGE_H_
 #define IPC_IPC_SYNC_MESSAGE_H_
 
 #include <stdint.h>
 
 #if defined(OS_WIN)
 #include <windows.h>
 #endif
 
 #include <memory>
 #include <string>
 
 #include "build/build_config.h"
 #include "ipc/ipc_message.h"
 
+namespace base {
+class WaitableEvent;
+}
+
 namespace IPC {
 
 class MessageReplyDeserializer;
-class MojoEvent;
 
 class IPC_EXPORT SyncMessage : public Message {
  public:
   SyncMessage(int32_t routing_id,
               uint32_t type,
               PriorityValue priority,
               MessageReplyDeserializer* deserializer);
   ~SyncMessage() override;
 
   // Call this to get a deserializer for the output parameters.
   // Note that this can only be called once, and the caller is responsible
   // for deleting the deserializer when they're done.
   MessageReplyDeserializer* GetReplyDeserializer();
 
   // If this message can cause the receiver to block while waiting for user
   // input (i.e. by calling MessageBox), then the caller needs to pump window
   // messages and dispatch asynchronous messages while waiting for the reply.
-  // This call enables message pumping behavior while waiting for a reply to
-  // this message.
-  void EnableMessagePumping() {
-    header()->flags |= PUMPING_MSGS_BIT;
+  // If this event is passed in, then window messages will start being pumped
+  // when it's set.  Note that this behavior will continue even if the event is
+  // later reset.  The event must be valid until after the Send call returns.
+  void set_pump_messages_event(base::WaitableEvent* event) {
+    pump_messages_event_ = event;
+    if (event) {
+      header()->flags |= PUMPING_MSGS_BIT;
+    } else {
+      header()->flags &= ~PUMPING_MSGS_BIT;
+    }
   }
 
-  // Indicates whether window messages should be pumped while waiting for a
-  // reply to this message.
-  bool ShouldPumpMessages() const {
-    return (header()->flags & PUMPING_MSGS_BIT) != 0;
+  // Call this if you always want to pump messages.  You can call this method
+  // or set_pump_messages_event but not both.
+  void EnableMessagePumping();
+
+  base::WaitableEvent* pump_messages_event() const {
+    return pump_messages_event_;
   }
 
   // Returns true if the message is a reply to the given request id.
   static bool IsMessageReplyTo(const Message& msg, int request_id);
 
   // Given a reply message, returns an iterator to the beginning of the data
   // (i.e. skips over the synchronous specific data).
   static base::PickleIterator GetDataIterator(const Message* msg);
 
   // Given a synchronous message (or its reply), returns its id.
   static int GetMessageId(const Message& msg);
 
   // Generates a reply message to the given message.
   static Message* GenerateReply(const Message* msg);
 
  private:
   struct SyncHeader {
     // unique ID (unique per sender)
     int message_id;
   };
 
   static bool ReadSyncHeader(const Message& msg, SyncHeader* header);
   static bool WriteSyncHeader(Message* msg, const SyncHeader& header);
 
   std::unique_ptr<MessageReplyDeserializer> deserializer_;
+  base::WaitableEvent* pump_messages_event_;
 };
 
 // Used to deserialize parameters from a reply to a synchronous message
 class IPC_EXPORT MessageReplyDeserializer {
  public:
   virtual ~MessageReplyDeserializer() {}
   bool SerializeOutputParameters(const Message& msg);
  private:
   // Derived classes need to implement this, using the given iterator (which
   // is skipped past the header for synchronous messages).
   virtual bool SerializeOutputParameters(const Message& msg,
                                          base::PickleIterator iter) = 0;
 };
 
 // When sending a synchronous message, this structure contains an object
 // that knows how to deserialize the response.
 struct PendingSyncMsg {
-  PendingSyncMsg(int id, MessageReplyDeserializer* d, MojoEvent* e)
+  PendingSyncMsg(int id,
+                 MessageReplyDeserializer* d,
+                 base::WaitableEvent* e)
       : id(id), deserializer(d), done_event(e), send_result(false) { }
-
   int id;
   MessageReplyDeserializer* deserializer;
-  MojoEvent* done_event;
+  base::WaitableEvent* done_event;
   bool send_result;
 };
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_SYNC_MESSAGE_H_