Snapshots: Add --extra-code flag to mksnapshot which lets you specify a file

Snapshots: Add --extra-code flag to mksnapshot which lets you specify a file
with more JS code that is loaded into the VM before writing the snapshot.  Get
rid of the hard coded limit on the partial snapshot cache size.  This change
disables most of the serializer tests for the snapshot build of the VM: It's
getting too complicated to support both booting from a snapshot and then
creating a new snapshot from the same VM or loading more code with another
snapshot in the same VM.
Review URL: http://codereview.chromium.org/10574013

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11871 ce2b1a6d-e550-0410-aec6-3dcde31c8c00