Use zero-copy external string resources for storing the built-in JS
source code. Saves a few hundred kilobyte of memory and consistently
speeds up `benchmark/misc/startup.js` by 2.5%.
Everything old is new again! Commit 74954ce ("Add string class that
uses ExternalAsciiStringResource.") from 2011 did the same thing but
I removed that in 2013 in commit 34b0a36 ("src: don't use NewExternal()
with unaligned strings") because of a limitation in the V8 API.
V8 no longer requires that strings are aligned if they are one-byte
strings so it should be safe to re-enable external strings again.
PR-URL: https://github.com/nodejs/node/pull/5458
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Robert Jefe Lindstaedt <robert.lindstaedt@gmail.com>
e4290dec2d