Unmounts volumes before writing to a drive.

chrome/browser/extensions/api/image_writer_private/destroy_partitions_operation.cc

 // Copyright 2014 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.
 
 #include "base/file_util.h"
 #include "chrome/browser/extensions/api/image_writer_private/destroy_partitions_operation.h"
 #include "chrome/browser/extensions/api/image_writer_private/error_messages.h"
 #include "content/public/browser/browser_thread.h"
 
 namespace extensions {
 namespace image_writer {
 
-// Number of bytes for the maximum partition table size.  By wiping this many
-// bytes we can essentially guarantee the header and associated information will
-// be wiped. See http://crbug.com/328246 for more information.
-const int kPartitionTableSize = 1 * 1024;
+// Number of bytes for the maximum partition table size.  GUID partition tables
+// reside in the second sector of the disk.  Disks can have up to 4k sectors.
+// See http://crbug.com/328246 for more information.
+const int kPartitionTableSize = 2 * 4096;
 
 DestroyPartitionsOperation::DestroyPartitionsOperation(
     base::WeakPtr<OperationManager> manager,
     const ExtensionId& extension_id,
     const std::string& storage_unit_id)
     : Operation(manager, extension_id, storage_unit_id) {}
 
 DestroyPartitionsOperation::~DestroyPartitionsOperation() {}
 
 void DestroyPartitionsOperation::StartImpl() {
@@ skipping 14 matching lines @@
   content::BrowserThread::PostTask(
       content::BrowserThread::FILE,
       FROM_HERE,
       base::Bind(&DestroyPartitionsOperation::Write,
                  this,
                  base::Bind(&DestroyPartitionsOperation::Finish, this)));
 }
 
 }  // namespace image_writer
 }  // namespace extensions