Revert "Use stability to only conditionally flush information from the CheckMaps table."

R=ishell@chromium.org

Review URL: https://codereview.chromium.org/180023002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19548 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix for failing asserts in HBoundsCheck code generation on x64: index register should be zero extended.

BUG=345820
LOG=N
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/180013002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19549 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Merge remote-tracking branch 'upstream/master'