V8 supports a mechanism to generate better profiling information for
ticks in bytecode execution. Usually, these would find the IET but would
not know which JS function is currently being executed. With
--interpreted_frames_native_stack, we create a dedicated copy of the
IET for each JS function, which the profiler can use the infer the
current function.

This mechanism doesn't work when IET is embedded. But JIT-less V8 will
require all builtins to be embedded.

This CL implements a workaround that should keep all configuration
happy: We keep a full copy of IET on the root list for sole purpose of
using it as a template to create copies for profiling later on. The
'real' IET builtin itself can be embedded in a follow-up CL.

Change-Id: Iaf1629708f0e41c3683979245019fbd3e3153c97
Reviewed-on: https://chromium-review.googlesource.com/c/1335700
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57548}