Adds USB writing for OS X.

chrome/utility/image_writer/image_writer_win.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 <windows.h>
 #include <setupapi.h>
 #include <winioctl.h>
 
 #include "chrome/utility/image_writer/error_messages.h"
 #include "chrome/utility/image_writer/image_writer.h"
@@ skipping 37 matching lines @@
     PLOG(ERROR) << "Storage property query failed";
     return false;
   }
 
   STORAGE_DEVICE_DESCRIPTOR* device_descriptor =
       reinterpret_cast<STORAGE_DEVICE_DESCRIPTOR*>(output_buf.get());
 
   return device_descriptor->RemovableMedia == TRUE;
 }
 
-bool ImageWriter::UnmountVolumes() {
+bool ImageWriter::OpenDevice() {
+  // Windows requires that device files be opened with FILE_FLAG_NO_BUFFERING
+  // and FILE_FLAG_WRITE_THROUGH.  These two flags are not part of base::File.
+  device_file_ =
+      base::File(CreateFile(device_path_.value().c_str(),
+                            GENERIC_READ | GENERIC_WRITE,
+                            FILE_SHARE_READ | FILE_SHARE_WRITE,
+                            NULL,
+                            OPEN_EXISTING,
+                            FILE_FLAG_NO_BUFFERING | FILE_FLAG_WRITE_THROUGH,
+                            NULL));
+  return device_file_.IsValid();
+}
+
+void ImageWriter::UnmountVolumes(const base::Closure& continuation) {
   if (!InitializeFiles()) {
     return false;
   }
 
   STORAGE_DEVICE_NUMBER sdn = {0};
   DWORD bytes_returned;
 
   BOOL status = DeviceIoControl(
       device_file_.GetPlatformFile(),
       IOCTL_STORAGE_GET_DEVICE_NUMBER,
@@ skipping 101 matching lines @@
         success = false;
         break;
       }
     }
   }
 
   if (volume_finder != INVALID_HANDLE_VALUE) {
     FindVolumeClose(volume_finder);
   }
 
-  return success;
+  if (success)
+    callback.Run();
 }
 
 }  // namespace image_writer