Support serializable DOMFileSystem on the V8-based structured clone path.

third_party/WebKit/Source/platform/FileSystemType.h

Index: third_party/WebKit/Source/platform/FileSystemType.h
diff --git a/third_party/WebKit/Source/platform/FileSystemType.h b/third_party/WebKit/Source/platform/FileSystemType.h
index 53be5aed65f56e3cd4024d527c2ef8461b221006..6c221a5abbb8cec11928bff0d3387d9a0c3a6f08 100644
--- a/third_party/WebKit/Source/platform/FileSystemType.h
+++ b/third_party/WebKit/Source/platform/FileSystemType.h
@@ -34,6 +34,10 @@
 namespace blink {
 
 // For file system types used in FileSystem API.
+//
+// WARNING: These enumerators can be serialized to disk (with IndexedDB).
+// If you have to update this list, also modify deserialization logic to handle
+// the previous version of this enum.

[haraken, 2016/10/20 14:51:57]

Nice catch!

 enum FileSystemType {
   FileSystemTypeTemporary,
   FileSystemTypePersistent,
@@ -43,6 +47,8 @@ enum FileSystemType {
 
   // Non-sandbox filesystem.
   FileSystemTypeExternal,
+
+  FileSystemTypeLast = FileSystemTypeExternal,
 };
 
 }  // namespace blink