If a child-to-parent IPCBlob is more than 1mb, we end up using a pipe stream.
If that ipcBlob is sent to a different process, we need to implement asyncWait
correctly: we need to call the remoteStream->AsyncWait().
IPCBlobInputStream must implement nsIIPCSerializableInputStream interface.
When this is done, the child sends the internal ID of the IPCBlobInputStream to
the parent.
IPCBlobInputStream is a new type of nsIInputStream that is used only in content
process when a Blob is sent from parent to child. This inputStream is for now,
just cloneable.
When the parent process sends a Blob to a content process, it has the Blob and
its inputStream. With its inputStream it creates a IPCBlobInputStreamParent
actor. This actor keeps the inputStream alive for following uses (not part of
this patch).
On the child side we will have, of course, a IPCBlobInputStreamChild actor.
This actor is able to create a IPCBlobInputStream when CreateStream() is
called. This means that 1 IPCBlobInputStreamChild can manage multiple
IPCBlobInputStreams each time one of them is cloned. When the last one of this
stream is released, the child actor sends a __delete__ request to the parent
side; the parent will be deleted, and the original inputStream, on the parent
side, will be released as well.
IPCBlobInputStream is a special inputStream because each method, except for
Available() fails. Basically, this inputStream cannot be used on the content
process for nothing else than knowing the size of the original stream.
In the following patches, I'll introduce an async way to use it.
