Add isWritableFileEntry to the fileSystem API

chrome/common/extensions/api/file_system.idl

Index: chrome/common/extensions/api/file_system.idl
diff --git a/chrome/common/extensions/api/file_system.idl b/chrome/common/extensions/api/file_system.idl
index f147956ed697095af985426daa972aa4606e0a22..51a93a6c39f3cea39c6afa53db43e625276a93b2 100644
--- a/chrome/common/extensions/api/file_system.idl
+++ b/chrome/common/extensions/api/file_system.idl
@@ -24,7 +24,8 @@ namespace fileSystem {
     DOMString? suggestedName;
   };
   callback GetDisplayPathCallback = void (DOMString displayPath);
-  callback FileEntryCallback = void ([instanceOf=fileEntry] object fileEntry);
+  callback FileEntryCallback = void ([instanceOf=FileEntry] object fileEntry);
+  callback IsWritableCallback = void (boolean isWritable);
 
   interface Functions {
     // Get the display path of a FileEntry object. The display path is based on
@@ -38,6 +39,10 @@ namespace fileSystem {
     static void getWritableFileEntry([instanceOf=FileEntry] object fileEntry,
                                      FileEntryCallback callback);
 
+    // Gets whether this FileEntry is writable or not.
+    static void isWritableFileEntry([instanceOf=FileEntry] object fileEntry,
+                                    IsWritableCallback callback);
+
     // Ask the user to choose a file.
     static void chooseFile(optional ChooseFileOptions options,
                            FileEntryCallback callback);