Fix an attachment broker race condition.

ipc/attachment_broker_privileged.h

 // Copyright 2015 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_ATTACHMENT_BROKER_PRIVILEGED_H_
 #define IPC_ATTACHMENT_BROKER_PRIVILEGED_H_
 
 #include <utility>
 #include <vector>
 
@@ skipping 53 matching lines @@
   // The lock returned by get_lock() must already be acquired before calling
   // this method. The return value is only guaranteed to be valid while the lock
   // is held.
   EndpointRunnerPair GetSenderWithProcessId(base::ProcessId id);
 
   // Sends a message to the endpoint, dispatching onto another thread if
   // necessary.
   void SendMessageToEndpoint(EndpointRunnerPair pair, Message* message);
 
   // Errors that can be reported by subclasses.
-  // These match tools/metrics/histograms.xml.
+  // These match tools/metrics/histograms/histograms.xml.
   // This enum is append-only.
   enum UMAError {
     // The brokerable attachment had a valid destination. This is the success
     // case.
     DESTINATION_FOUND = 0,
     // The brokerable attachment had a destination, but the broker did not have
     // a channel of communication with that process.
     DESTINATION_NOT_FOUND = 1,
     // The brokerable attachment did not have a destination process.
     NO_DESTINATION = 2,
@@ skipping 16 matching lines @@
     // Couldn't extract a right from the source.
     ERROR_EXTRACT_SOURCE_RIGHT = 11,
     // The broker did not have a channel of communication with the source
     // process.
     ERROR_SOURCE_NOT_FOUND = 12,
     // The broker could not open the source or destination process with extra
     // privileges.
     ERROR_COULD_NOT_OPEN_SOURCE_OR_DEST = 13,
     // The broker was asked to transfer a HANDLE with invalid permissions.
     ERROR_INVALID_PERMISSIONS = 14,
+    // The broker was not immediately able to send an attachment.
+    DELAYED = 15,
+    // The broker successfully sent a delayed attachment.
+    DELAYED_SEND = 16,
     ERROR_MAX
   };
 
   // Emits an UMA metric.
   void LogError(UMAError error);
 
  private:
   // A vector of Endpoints, and the SingleThreadTaskRunner that should be used
   // to invoke Send() on each Endpoint.
   std::vector<EndpointRunnerPair> endpoints_;
   DISALLOW_COPY_AND_ASSIGN(AttachmentBrokerPrivileged);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_ATTACHMENT_BROKER_PRIVILEGED_H_