Port https://chromium-review.googlesource.com/c/v8/v8/+/838403 to MIPS. Please assign this issue to me.

The following revision refers to this bug:
  https://chromium.googlesource.com/v8/v8.git/+/8e7527aa2ff1065fe3c1653973e329684de49c9e

commit 8e7527aa2ff1065fe3c1653973e329684de49c9e
Author: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Date: Fri Jan 26 14:20:33 2018

MIPS[64]: Port `[wasm] Implement wasm sign extension opcodes`

Port 1abeb5a3b1494be6212f934144b0e8584433f006

Change-Id: Ib31abb7e5e920b319d0e485bf5bcc29fdc018bbc
Bug:  chromium:806078 
Reviewed-on: https://chromium-review.googlesource.com/888744
Reviewed-by: Miran Karić <miran.karic@mips.com>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#50902}
[modify] https://crrev.com/8e7527aa2ff1065fe3c1653973e329684de49c9e/src/compiler/mips/instruction-selector-mips.cc
[modify] https://crrev.com/8e7527aa2ff1065fe3c1653973e329684de49c9e/src/compiler/mips64/instruction-selector-mips64.cc
[modify] https://crrev.com/8e7527aa2ff1065fe3c1653973e329684de49c9e/test/cctest/wasm/test-run-wasm-sign-extension.cc