Fix use-after-free bug in debugger

Fix use-after-free bug in debugger

This was the cause for crashes on Linux.
Committed: https://code.google.com/p/dart/source/detail?r=5668

[hausner, 2012-03-19 22:27:27]

Small fix. Thank you.

[siva, 2012-03-19 22:45:21]

LGTM with question regarding removal of internal breakpoints on certain paths.

http://codereview.chromium.org/9726017/diff/1/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

http://codereview.chromium.org/9726017/diff/1/runtime/vm/debugger.cc#newcode528
runtime/vm/debugger.cc:528: if (!target_function.HasCode()) {
If this path is taken internal breakpoints would not be deleted. 
Maybe there should be a RemoveInternalBreakpoints() here too.

http://codereview.chromium.org/9726017/diff/1/runtime/vm/debugger.cc#newcode912
runtime/vm/debugger.cc:912: }
What happens if code.IsNull() is true? (internal breakpoints not removed).

http://codereview.chromium.org/9726017/diff/1/runtime/vm/debugger.cc#newcode924
runtime/vm/debugger.cc:924: }
What about the case when stack_trace->Length() == 1? (internal breakpoints not
removed).

http://codereview.chromium.org/9726017/diff/1/runtime/vm/debugger.cc#newcode931
runtime/vm/debugger.cc:931: InstrumentForStepping(caller->DartFunction());
Ditto question.

[hausner, 2012-03-19 23:35:15]

Thank you. I separated the BP removal and instrumenting again. TAL if you like.

http://codereview.chromium.org/9726017/diff/1/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

http://codereview.chromium.org/9726017/diff/1/runtime/vm/debugger.cc#newcode528
runtime/vm/debugger.cc:528: if (!target_function.HasCode()) {
On 2012/03/19 22:45:22, asiva wrote:
> If this path is taken internal breakpoints would not be deleted. 
> Maybe there should be a RemoveInternalBreakpoints() here too.

See comments below.

http://codereview.chromium.org/9726017/diff/1/runtime/vm/debugger.cc#newcode912
runtime/vm/debugger.cc:912: }
On 2012/03/19 22:45:22, asiva wrote:
> What happens if code.IsNull() is true? (internal breakpoints not removed).

Ok, mixing the instrumenting function and deleting temp breakpoints was a bad
idea. I added explicit calls again here.

http://codereview.chromium.org/9726017/diff/1/runtime/vm/debugger.cc#newcode924
runtime/vm/debugger.cc:924: }
On 2012/03/19 22:45:22, asiva wrote:
> What about the case when stack_trace->Length() == 1? (internal breakpoints not
> removed).
Ditto.

http://codereview.chromium.org/9726017/diff/1/runtime/vm/debugger.cc#newcode931
runtime/vm/debugger.cc:931: InstrumentForStepping(caller->DartFunction());
On 2012/03/19 22:45:22, asiva wrote:
> Ditto question.
Ditto.

[siva, 2012-03-19 23:55:44]

LGTM