The Run() method ran in chunks of {kRunSteps} steps till completion or
breakpoint, while Step() executed exactly one step.
This CL removes the {kRunSteps} concept, and instead allows to pass the
number of steps to run to the Run() method. Step() just calls Run(1).

R=ahaas@chromium.org
BUG=chromium:708457,v8:5822

Change-Id: I03f7f4da4e0d0e72337399206f1c49ff0f1f041a
Reviewed-on: https://chromium-review.googlesource.com/469846
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44443}