Add support for lists and backward references when decoding a message to a Dart_CObject object

Add support for lists and backward references when decoding a message to a Dart_CObject object

The C message reader can now read lists created like this: 

  new List() 
  new List<int>() 
  new List<String>() 
  new List<double>() 
  new List<bool>() 

The backward references are now resolved and already allocated
Dart_CObject objects are reused when there is a backward reference.

The reuse of the Dart_CObject objects poses the issue of which objects
where allocated with the supplied allocator and which where not.

Currently this will work best with a zone allocator. This will be added
to the tests in a subsequent change.

R=asiva@google.com, turnidge@google.com

BUG=
TEST=

Committed: https://code.google.com/p/dart/source/detail?r=3831

[Søren Gjesse, 2012-01-31 12:17:49]

This is based on https://chromiumcodereview.appspot.com/9303001/.

[siva, 2012-02-02 04:01:57]

LGTM

The issue of freeing reused objects in the unit tests at least can be solved by
uzing a ZoneAllocator. As indicated in the other CL the native message handler
that Todd is providing will take care of allocation and free of the Cobject
after it issues the Callback

https://chromiumcodereview.appspot.com/9303031/diff/1/runtime/vm/snapshot.cc
File runtime/vm/snapshot.cc (right):

https://chromiumcodereview.appspot.com/9303031/diff/1/runtime/vm/snapshot.cc#...
runtime/vm/snapshot.cc:633: // TODO(sgjesse): Handle back-references.
You are handling backward references now, the TODO can go.

https://chromiumcodereview.appspot.com/9303031/diff/1/runtime/vm/snapshot.cc#...
runtime/vm/snapshot.cc:638: UNREACHABLE();
Is the UNREACHABLE needed?

https://chromiumcodereview.appspot.com/9303031/diff/1/runtime/vm/snapshot_tes...
File runtime/vm/snapshot_test.cc (right):

https://chromiumcodereview.appspot.com/9303031/diff/1/runtime/vm/snapshot_tes...
runtime/vm/snapshot_test.cc:947: free(object);
Here too if GetDesrializedDartObject used a ZoneAllocator then you would not
have to bother with freeing the Cobjects that were created.

[Søren Gjesse, 2012-02-02 09:59:49]

I had to combine this with  https://chromiumcodereview.appspot.com/9303001/
(adding support for lists) as this depended on it.

https://chromiumcodereview.appspot.com/9303031/diff/1/runtime/vm/snapshot.cc
File runtime/vm/snapshot.cc (right):

https://chromiumcodereview.appspot.com/9303031/diff/1/runtime/vm/snapshot.cc#...
runtime/vm/snapshot.cc:633: // TODO(sgjesse): Handle back-references.
On 2012/02/02 04:01:57, asiva wrote:
> You are handling backward references now, the TODO can go.

Done.

https://chromiumcodereview.appspot.com/9303031/diff/1/runtime/vm/snapshot.cc#...
runtime/vm/snapshot.cc:638: UNREACHABLE();
On 2012/02/02 04:01:57, asiva wrote:
> Is the UNREACHABLE needed?

No, removed.

https://chromiumcodereview.appspot.com/9303031/diff/1/runtime/vm/snapshot_tes...
File runtime/vm/snapshot_test.cc (right):

https://chromiumcodereview.appspot.com/9303031/diff/1/runtime/vm/snapshot_tes...
runtime/vm/snapshot_test.cc:947: free(object);
On 2012/02/02 04:01:57, asiva wrote:
> Here too if GetDesrializedDartObject used a ZoneAllocator then you would not
> have to bother with freeing the Cobjects that were created.

Moving to a zone allocator is part up later CL.