Small cleanup: AstConstructionVisitor no longer needs a Zone pointer.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/265623002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21088 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Do not use default for switch over AllocationSpace.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/262583004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21089 ce2b1a6d-e550-0410-aec6-3dcde31c8c00