Add Dart stack walker

Add Dart stack walker that relies on frame pointers.

* It is used only when we don't have a top exit frame and we have the script tag set.
* Steps across exit frames and only collects Dart frames.

R=asiva@google.com

Committed: https://code.google.com/p/dart/source/detail?r=38475

[siva, 2014-07-22 20:31:12]

lgtm

https://chromiumcodereview.appspot.com/408663004/diff/1/runtime/vm/profiler.cc
File runtime/vm/profiler.cc (right):

https://chromiumcodereview.appspot.com/408663004/diff/1/runtime/vm/profiler.c...
runtime/vm/profiler.cc:1783: }
set pc_ only after determining that you are about to return true and in the
false return above restore fp_ back to old state ?

https://chromiumcodereview.appspot.com/408663004/diff/1/runtime/vm/profiler.c...
runtime/vm/profiler.cc:1803: }
In all the case where you return false, I feel you should restore fp_ back to
the original value, i.e: fp_ = old_fp;

https://chromiumcodereview.appspot.com/408663004/diff/1/runtime/vm/profiler.c...
runtime/vm/profiler.cc:1809: ASSERT(sp_ != NULL);
Probably need to assert 

ASSERT(FindCodeForPC(*sp_) != Code::null());

FindCodeForPC is a function you seem to have elsewhere in this file.

[Cutch, 2014-07-22 20:50:12]

https://chromiumcodereview.appspot.com/408663004/diff/1/runtime/vm/profiler.cc
File runtime/vm/profiler.cc (right):

https://chromiumcodereview.appspot.com/408663004/diff/1/runtime/vm/profiler.c...
runtime/vm/profiler.cc:1783: }
On 2014/07/22 20:31:12, siva wrote:
> set pc_ only after determining that you are about to return true and in the
> false return above restore fp_ back to old state ?

Done.

https://chromiumcodereview.appspot.com/408663004/diff/1/runtime/vm/profiler.c...
runtime/vm/profiler.cc:1803: }
On 2014/07/22 20:31:12, siva wrote:
> In all the case where you return false, I feel you should restore fp_ back to
> the original value, i.e: fp_ = old_fp;

Done.

https://chromiumcodereview.appspot.com/408663004/diff/1/runtime/vm/profiler.c...
runtime/vm/profiler.cc:1809: ASSERT(sp_ != NULL);
On 2014/07/22 20:31:12, siva wrote:
> Probably need to assert 
> 
> ASSERT(FindCodeForPC(*sp_) != Code::null());
> 
> FindCodeForPC is a function you seem to have elsewhere in this file.

It's not guaranteed that we are reading a PC from the stack.

[Cutch, 2014-07-22 21:08:27]

Committed patchset #2 manually as r38475 (presubmit successful).