Port e3e3480b

Original Commit Message:

    The builtins table is an array of pointers to builtin code objects. It
    used to be located within the Builtins class, which itself was part of
    the Isolate.

    To enable faster isolate-independent access to builtin code objects,
    this CL moves the builtins table into the heap, at a constant known
    offset from the roots table. With this change, builtins can be accessed
    through the root pointer with a single instruction:

     mov reg, [kRootPointer, <offset to builtin>]

    TurboAssembler::LookupConstant is also extended in this CL to
    potentially shortcut the slow-ish constants table lookup: root
    constants are loaded through the root list, and builtin constants
    through the builtins table.

R=jgruber@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: I1dac4ad30960d50f77aba7ec7da63b1f1259613d
Reviewed-on: https://chromium-review.googlesource.com/1087410Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#53532}