Next bunch of fixes for check elimination.

- Canonicalize HCheckMapValue with constant map to
  HCheckMaps, and get rid of the special treatment
  during check elimination.
- Track only stable object maps for HConstants and
  add CHECK()s to verify state during code generation.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/263923004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21154 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix Mac64-debug issue introduced with r21154.

R=ishell@chromium.org

Review URL: https://codereview.chromium.org/271443002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21155 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
ARM64: Use default-NaN mode to canonicalize NaNs.

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/255343004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21156 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Make sure CPU profiler collects a sample on start.

BUG=369035
LOG=N
R=bmeurer@chromium.org, yurys@chromium.org

Review URL: https://codereview.chromium.org/263883008

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21157 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Do not call setters of read-only accessors.

BUG=
TEST=mjsunit/readonly-accessor
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/271433002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21158 ce2b1a6d-e550-0410-aec6-3dcde31c8c00