Fix constructors for HLoadNamedField.

Also try to determine an appropriate HType for tracked fields,
instead of (incorrectly) using HType::NonPrimitive() everywhere.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/269353003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21186 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Turn CHECK()s into ASSERT()s.

R=machenbach@chromium.org

Review URL: https://codereview.chromium.org/275433002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21187 ce2b1a6d-e550-0410-aec6-3dcde31c8c00