Fixes issues raised after committing the following CLs: https://codereview.chromium.org/1649053002 https://codereview.chromium.org/1647113003 Also generates a trap instruction if hybrid assembly is turned off, and the skip implementation command line flag is turned on. BUG=None R=stichnot@chromium.org Review URL: https://codereview.chromium.org/1654483002 .
