We reuse most of the infrastructure to set break points, with minor
differences when we encounter functions where we can only break on entry:
- PrepareFunctionForBreakPoints simply deopts all functions.
- Break point objects have the canonical source position 0.
- Break point is set/checked/cleared via bit on the DebugInfo.
- Debug::Break do not continue stepping since stepping is implemented via
  regular break points and therefore do not interfere with break on entry.

I promise to add more tests.

Bug: v8:178
Change-Id: Ifc8231995c771286db0b848b811e1c3ad3b12494
Reviewed-on: https://chromium-review.googlesource.com/906245
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51152}