Adds removable-drive listing for OS X.

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

Index: chrome/browser/extensions/api/image_writer_private/removable_storage_provider.cc
diff --git a/chrome/browser/extensions/api/image_writer_private/removable_storage_provider.cc b/chrome/browser/extensions/api/image_writer_private/removable_storage_provider.cc
index 536a60074be6252414435bdc72c781d264d555d9..e62bd106b42ad4e1d57739dc02b252af24bb9f83 100644
--- a/chrome/browser/extensions/api/image_writer_private/removable_storage_provider.cc
+++ b/chrome/browser/extensions/api/image_writer_private/removable_storage_provider.cc
@@ -4,6 +4,7 @@
 // found in the LICENSE file.
 
 #include "base/lazy_instance.h"
+#include "base/message_loop/message_loop.h"
 #include "chrome/browser/extensions/api/image_writer_private/removable_storage_provider.h"
 #include "content/public/browser/browser_thread.h"
 
@@ -15,23 +16,15 @@ static base::LazyInstance<scoped_refptr<StorageDeviceList> > g_test_device_list;
 // TODO(haven): Udev code may be duplicated in the Chrome codebase.
 // https://code.google.com/p/chromium/issues/detail?id=284898
 
-void RemovableStorageProvider::GetAllDevices(DeviceListReadyCallback callback) {
+void RemovableStorageProvider::GetAllDevices(
+    const DeviceListReadyCallback& callback) {
   if (g_test_device_list.Get() != NULL) {
-    content::BrowserThread::PostTask(
-        content::BrowserThread::FILE,
-        FROM_HERE,
-        base::Bind(callback, g_test_device_list.Get(), true));
+    base::MessageLoop::current()->PostTask(
+        FROM_HERE, base::Bind(callback, g_test_device_list.Get(), true));
     return;
   }
 
-  scoped_refptr<StorageDeviceList> device_list(new StorageDeviceList);
-
-  // We need to do some file i/o to get the device block size
-  content::BrowserThread::PostTaskAndReplyWithResult(
-      content::BrowserThread::FILE,
-      FROM_HERE,
-      base::Bind(PopulateDeviceList, device_list),
-      base::Bind(callback, device_list));
+  GetAllDevicesImpl(callback);
 }
 
 void RemovableStorageProvider::SetDeviceListForTesting(