The thread local key for assert scopes can be lazily initialized and
should be independent of the Isolate initialization. Also cleanup the
assert-scope.{cc,h} implementation while I was at it.

R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/609253002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24275 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

- this avoids using relative include paths which are forbidden by the style guide
- makes the code more readable since it's clear which header is meant
- allows for starting to use checkdeps

BUG=none
R=jkummerow@chromium.org, danno@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/304153016

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21625 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

R=jochen@chromium.org

Review URL: https://codereview.chromium.org/198253004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20062 ce2b1a6d-e550-0410-aec6-3dcde31c8c00