Adds USB writing for OS X.

chrome/utility/image_writer/image_writer_win.cc

Index: chrome/utility/image_writer/image_writer_win.cc
diff --git a/chrome/utility/image_writer/image_writer_win.cc b/chrome/utility/image_writer/image_writer_win.cc
index b3cec9507445bc47ec1e83f2869e6abb38dd3b04..1d6542e5e3f030e5659e7ecccd45ff32485203aa 100644
--- a/chrome/utility/image_writer/image_writer_win.cc
+++ b/chrome/utility/image_writer/image_writer_win.cc
@@ -55,7 +55,21 @@ bool ImageWriter::IsValidDevice() {
   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;
   }
@@ -177,7 +191,8 @@ bool ImageWriter::UnmountVolumes() {
     FindVolumeClose(volume_finder);
   }
 
-  return success;
+  if (success)
+    callback.Run();
 }
 
 }  // namespace image_writer