Move more builtin files to strict mode.

R=rossberg@chromium.org
BUG=v8:1955
LOG=N

Review URL: https://codereview.chromium.org/279543002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21254 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Make escape analysis preserve all representations required by HCompareNumericAndBranch.

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/257803012

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21255 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Harden %SetIsObserved with RUNTIME_ASSERTs

Now throws if its argument is already observed, or if the argument is
the global proxy.

BUG=371782
LOG=Y
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/274163002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21256 ce2b1a6d-e550-0410-aec6-3dcde31c8c00