[turbofan] Support initial step-in through debugger statement.

[turbofan] Support initial step-in through debugger statement.

This adapts the debugger so that the first break event starting the
stepping process can come from optimized code. TurboFan supports a
debugger statement and hence can be the top-most frame whenever the
Debug::HandleDebugBreak handler is triggered.

R=yangguo@chromium.org
TEST=mjsunit/debug,cctest/test-debug

Committed: https://crrev.com/7d0e5593e5a88285b109cd4d75ca15c4c0721ce9
Cr-Commit-Position: refs/heads/master@{#27447}

[Yang, 2015-03-25 13:58:34]

On 2015/03/25 12:21:10, Michael Starzinger wrote:

LGTM. Not sure whether we need a test case that specifically tests a function
with debugger statement. The ones you un-blacklisted probably already test that
with --always-opt.

[Michael Starzinger, 2015-03-25 14:37:50]

On 2015/03/25 13:58:34, Yang wrote:
> LGTM. Not sure whether we need a test case that specifically tests a function
> with debugger statement. The ones you un-blacklisted probably already test
that
> with --always-opt.

Yes, essentially all the newly enabled test cases follow exactly that pattern.

[Michael Starzinger, 2015-03-25 14:54:48]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-03-25 14:55:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1038613002/2

[commit-bot: I haz the power, 2015-03-25 15:02:35]

Committed patchset #2 (id:2)

[commit-bot: I haz the power, 2015-03-25 15:02:54]

Patchset 2 (id:??) landed as
https://crrev.com/7d0e5593e5a88285b109cd4d75ca15c4c0721ce9
Cr-Commit-Position: refs/heads/master@{#27447}