MIPS64: Fix MULT in simulator to conform the spec.

TEST=mjsunit/numops-fuzz-part4
BUG=
R=balazs.kilvady@imgtec.com

Review URL: https://codereview.chromium.org/756073003

Cr-Commit-Position: refs/heads/master@{#25568}
De-generify the GenericGraph.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/767733002

Cr-Commit-Position: refs/heads/master@{#25569}
Introduce a kill-switch for shipping features.

R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/763273002

Cr-Commit-Position: refs/heads/master@{#25570}
Expose generator object internal properties via mirrors.

BUG=v8:3292
R=yangguo@chromium.org, wingo@igalia.com
LOG=N

Review URL: https://codereview.chromium.org/760303002

Cr-Commit-Position: refs/heads/master@{#25571}
De-generify the GenericNode.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/756073004

Cr-Commit-Position: refs/heads/master@{#25572}