This is UI side unreadable device support.

chrome/browser/extensions/extension_file_browser_private_api.h

Index: chrome/browser/extensions/extension_file_browser_private_api.h
diff --git a/chrome/browser/extensions/extension_file_browser_private_api.h b/chrome/browser/extensions/extension_file_browser_private_api.h
index 7c7716dfe228003d9691b9a592efbad1cfe152a9..f92664ec805d204185d395548863e2ffc355d066 100644
--- a/chrome/browser/extensions/extension_file_browser_private_api.h
+++ b/chrome/browser/extensions/extension_file_browser_private_api.h
@@ -296,6 +296,21 @@ class FormatDeviceFunction
   DECLARE_EXTENSION_FUNCTION_NAME("fileBrowserPrivate.formatDevice");
 };
 
+// Formats Device given its file path.
+class FormatUnmountedDeviceFunction
+    : public SyncExtensionFunction {
+ public:
+  FormatUnmountedDeviceFunction();
+
+ protected:
+  virtual ~FormatUnmountedDeviceFunction();
+
+  virtual bool RunImpl() OVERRIDE;
+
+ private:
+  DECLARE_EXTENSION_FUNCTION_NAME("fileBrowserPrivate.formatUnmountedDevice");
+};
+
 // Retrieves devices meta-data. Expects volume's device path as an argument.
 class GetVolumeMetadataFunction
     : public SyncExtensionFunction {