[turbofan] extend register allocator testing with control flow

R=bmeurer@chromium.org, jarin@chromium.org

BUG=

Review URL: https://codereview.chromium.org/699083003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25178 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Retry: Parser & internalization fix: ensure no heap allocs during GetString(Handle<String>).

The bug has always been there: when the parser is operating in the "immediately
internalize" mode and calls GetString, we get FlatContent of a string and then
do heap allocation.

The bug was uncovered by https://codereview.chromium.org/693803004/ (which put
the parser to the "immediately internalize" mode more often), but looking at the
code, it's possible that it can happen in other cases too.

This CL makes AstValueFactory handle this situation gracefully: it won't try to
internalize inside GetString(Handle<String>); it's unnecessary anyway since we
have the Handle<String> already.

BUG=
R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/706533005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25179 ce2b1a6d-e550-0410-aec6-3dcde31c8c00