- Remove obsolete BreakLocatorType.
- Perform PrepareStepOnThrow after OnException event, in case stepping
  was scheduled in the exception event.
- Use frame count instead of frame pointer for stepping. Frame pointer
  is not reliable due to possible deopts.
- Consistently check for inlined functions in inlined frames.
- Use SharedFunctionInfo in FloodWithOneshot and EnsureDebugInfo.

R=jgruber@chromium.org
BUG=v8:5901

Review-Url: https://codereview.chromium.org/2664793002
Cr-Commit-Position: refs/heads/master@{#42878}