This CL removes the code specialization for WASM functions that access
globals. Previously, we were embedding the start address of the globals
memory (globals_start) as a constant in the code, which required
patching for every instance. We now put this base in to the WasmContext,
which is available as a parameter to every WasmFunction.

R=ahaas@chromium.org,
CC=mtrofin@chromium.org

Bug: 
Change-Id: I04bb739e898cc5a3b7dd081cc166483022d113fd
Reviewed-on: https://chromium-review.googlesource.com/712595
Commit-Queue: Ben Titzer <titzer@chromium.org>
Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48581}