diff --git a/dom/ipc/DOMTypes.ipdlh b/dom/ipc/DOMTypes.ipdlh
index 794056aef590..8a6bdf49b051 100644
--- a/dom/ipc/DOMTypes.ipdlh
+++ b/dom/ipc/DOMTypes.ipdlh
@@ -44,6 +44,116 @@ struct ClonedMessageData
   MessagePortIdentifier[] identfiers;
 };
 
+// I could remove this completely, but this will be gone in the following patch.
+union BlobDataStream
+{
+  IPCStream;
+};
+
+union BlobData
+{
+  // For remote blobs.
+  nsID;
+
+  // For memory-backed blobs.
+  BlobDataStream;
+
+  // For multiplex blobs.
+  BlobData[];
+};
+
+union OptionalBlobData
+{
+  BlobData;
+  void_t;
+};
+
+struct NormalBlobConstructorParams
+{
+  nsString contentType;
+  uint64_t length;
+
+  // This must be of type BlobData in a child->parent message, and will always
+  // be of type void_t in a parent->child message.
+  OptionalBlobData optionalBlobData;
+};
+
+struct FileBlobConstructorParams
+{
+  nsString name;
+  nsString contentType;
+  nsString path;
+  uint64_t length;
+  int64_t modDate;
+  bool isDirectory;
+
+  // This must be of type BlobData in a child->parent message, and will always
+  // be of type void_t in a parent->child message.
+  OptionalBlobData optionalBlobData;
+};
+
+struct SlicedBlobConstructorParams
+{
+  // broken structure: PBlob source;
+  nsID id;
+  uint64_t begin;
+  uint64_t end;
+  nsString contentType;
+};
+
+struct MysteryBlobConstructorParams
+{
+  // Nothing is known about this type of blob.
+};
+
+struct KnownBlobConstructorParams
+{
+  nsID id;
+};
+
+// This may only be used for same-process inter-thread communication!
+struct SameProcessBlobConstructorParams
+{
+  // This member should be reinterpret_cast'd to mozilla::dom::BlobImpl. It
+  // carries a reference.
+  intptr_t addRefedBlobImpl;
+};
+
+union AnyBlobConstructorParams
+{
+  // These types may be sent to/from parent and child.
+  NormalBlobConstructorParams;
+  FileBlobConstructorParams;
+  SameProcessBlobConstructorParams;
+
+  // This type may only be sent from parent to child.
+  MysteryBlobConstructorParams;
+
+  // These types may only be sent from child to parent.
+  SlicedBlobConstructorParams;
+  KnownBlobConstructorParams;
+};
+
+struct ChildBlobConstructorParams
+{
+  nsID id;
+
+  // May not be SlicedBlobConstructorParams or KnownBlobConstructorParams.
+  AnyBlobConstructorParams blobParams;
+};
+
+struct ParentBlobConstructorParams
+{
+  // May not be MysteryBlobConstructorParams.
+  AnyBlobConstructorParams blobParams;
+};
+
+union BlobConstructorParams
+{
+  ChildBlobConstructorParams;
+  ParentBlobConstructorParams;
+};
+
 union IPCDataTransferData
 {
   nsString;  // text