An IPCBlobInputStream can be sent back to the parent process (not implemented
in this patch). When this is done, we basically send only the internal ID.
From this ID, we can retrieve the original inputStream because any
IPCBlobInputStreamParent actor has previously registered it into a singleton:
IPCBlobInputStreamStorage.
So, if we have a IPCBlobInputStreamParent, we have an inputStream, and this
inputStream is known by IPCBlobInputStreamStorage. This will be useful in the
next patches.
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.
This first patch introduces the basic idea of the refactoring. Instead of
having a PBlob protocol, here we have a simple IPC struct: IPCBlob.
When a Blob is sent to a different process, we move an IPCBlob struct with
type, size, some specific File properties, and an inputStream as IPCStream.
