Ensure the debugger keeps a reference to code objects

Ensure the debugger keeps a reference to code objects

Keep the code object in a breakpoint object rather than the
function object. This ensures that the GC can’t collect the
code object while there are breakpoints for the function.

R=zra@google.com

Committed: https://code.google.com/p/dart/source/detail?r=32006

[hausner, 2014-01-24 22:28:25]

Additional question: would it make sense to add a function that checks whether
there are breakpoints in a given code object, and use that in
RawFunction::SkipCode() ?

[zra, 2014-01-24 23:04:13]

lgtm with small comment.

If there's already a reference to the code object cached in the breakpoint
object, then I don't think it's strictly necessary, but since this is somewhat
delicate code, I think it's a good idea to have the extra check.

https://codereview.chromium.org/143263012/diff/1/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

https://codereview.chromium.org/143263012/diff/1/runtime/vm/debugger.cc#newco...
runtime/vm/debugger.cc:972: Code& code =
Code::Handle(target_function.unoptimized_code());
If there might be a GC during DeoptimizeWorld, then create this handle before.

[hausner, 2014-01-24 23:54:30]

Added Code::HasBreakpoint() and addressed comment.

https://codereview.chromium.org/143263012/diff/1/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

https://codereview.chromium.org/143263012/diff/1/runtime/vm/debugger.cc#newco...
runtime/vm/debugger.cc:972: Code& code =
Code::Handle(target_function.unoptimized_code());
On 2014/01/24 23:04:14, zra wrote:
> If there might be a GC during DeoptimizeWorld, then create this handle before.

Done.

[hausner, 2014-01-24 23:55:17]

Committed patchset #3 manually as r32006 (presubmit successful).