No compiler support for now (BTW: %_NewString, doesn't have that,
either), inline allocation will come later. Hopefully the last
intrisic to add for a StringAddStub POC...
Review URL: https://codereview.chromium.org/1041723002
Cr-Commit-Position: refs/heads/master@{#27508}
These are needed (among other things) for a TurboFan-generated
StringAddStub. Furthermore, they can be used to nuke the overly
complex %_IsInstanceType intrisic, it's completely expressible in
JavaScript now, but that will be done in a separate CL.
Alpha-sorted things a bit on the way to ease navigation.
Review URL: https://codereview.chromium.org/1010973010
Cr-Commit-Position: refs/heads/master@{#27415}
