Linux perf tool support update + refactoring.

This adds timestamps to allow profiling with code space reuse. Also a couple of updates to reflect the changes in the JIT perf interface + a move of the perf-related stuff into separate files.

Unfortunately, the change only works with the latest patch  to the perf tool from a Linux perf tool contributor (Stephane Eranian).

BUG=
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/255803003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22098 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
ES6: Add missing Set.prototype.keys function

https://people.mozilla.org/~jorendorff/es6-draft.html#sec-set.prototype.keys

The value of the keys property is just the initial value of the values
function.

BUG=v8:3411
LOG=Y
R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/353293003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22099 ce2b1a6d-e550-0410-aec6-3dcde31c8c00