Now that the BytecodeGenerator has a dedicated register holding
the generator object, BytecodeGenerator::VisitSuspend can
access the generator directly from that register. This reduces
by one the number of live registers at each suspend point.

Bug: v8:6351, v8:6460
Change-Id: I380a9d2bd8ca7eec6720e5392c1ca07dd0df0e2d
Reviewed-on: https://chromium-review.googlesource.com/522982
Commit-Queue: Adam Klein <adamk@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45710}