Drop dispatch_release(): ARC manages dispatch queues with a deployment target >= 10.8

chrome/installer/mac/app/Unpacker.m

 // Copyright 2016 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.
 
 #import "Unpacker.h"
 
 #import <AppKit/AppKit.h>
 #include <DiskArbitration/DiskArbitration.h>
 #include <dispatch/dispatch.h>
 
@@ skipping 128 matching lines @@
                 kDADiskUnmountOptionWhole | kDADiskUnmountOptionForce,
                 unmount_callback, (__bridge_retained void*)self);
 
   CFRelease(whole_disk);
   CFRelease(child_disk);
 }
 
 - (void)didFinishEjectingDisk:(DADiskRef)disk
                 withDissenter:(DADissenterRef)dissenter {
   DASessionSetDispatchQueue(session_, NULL);
+#if MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_8
   dispatch_release(unpack_dq_);
+#endif
   CFRelease(session_);
   NSError* error = nil;
   if (dissenter) {
     DAReturn status = DADissenterGetStatus(dissenter);
     error = [NSError
         errorWithDomain:@"ChromeErrorDomain"
                    code:err_get_code(status)
                userInfo:@{
                  NSLocalizedDescriptionKey :
                      (__bridge NSString*)DADissenterGetStatusString(dissenter)
                }];
     [delegate_ unpacker:self onUnmountFailure:error];
   } else {
     [self cleanUp];
     [delegate_ unpacker:self onUnmountSuccess:mountPath_];
   }
 }
 
 @end