RegExpExecStub pushes callee-saved registers without setting up a frame. This confuses the stack iterator.
Other architectures do not save these registers.
BUG=chromium:487981
LOG=NO
TEST=mjsunit/regress/regress-487981
Review URL: https://codereview.chromium.org/1183593005
Cr-Commit-Position: refs/heads/master@{#29120}
