Grouping all map creation code.

Grouping all map creation code.

- Now tunnel all descriptor changes through methods on the map
- Renamed CopyDropTransitions to regular Copy since we always "drop transitions" on copy anyway.
- Merged and moved elements transition map creation.

Committed: https://code.google.com/p/v8/source/detail?r=12105

[Toon Verwaest, 2012-07-17 12:35:19]

PTAL.

Main new methods are:
- Map::CopyAsElementsKind (from CreateNextElementsTransition)
- Map::Copy(Add|Insert|Replace)Descriptor

All those methods now take a flag as input that specifies whether they also want
to be stored as a transition or not.

[Jakob Kummerow, 2012-07-17 13:43:10]

LGTM with nits.

https://chromiumcodereview.appspot.com/10780031/diff/1/src/heap.cc
File src/heap.cc (right):

https://chromiumcodereview.appspot.com/10780031/diff/1/src/heap.cc#newcode3717
src/heap.cc:3717: { MaybeObject* maybe_prototype =
AllocateJSObjectFromMap(new_map);
nit: for consistency, remove this {} too, please.

https://chromiumcodereview.appspot.com/10780031/diff/1/src/heap.cc#newcode3726
src/heap.cc:3726: if (!maybe_result->To(&result)) return maybe_result;
Unless I'm missing something, this should rather be "if
(maybe_result->IsFailure()) ...", right? Which would make "Object* result;"
unnecessary, and maybe_result should then probably be called maybe_failure.

https://chromiumcodereview.appspot.com/10780031/diff/1/src/runtime.cc
File src/runtime.cc (right):

https://chromiumcodereview.appspot.com/10780031/diff/1/src/runtime.cc#newcode...
src/runtime.cc:2184: function->map()->CopyReplaceDescriptor(&new_desc,
nit: if you want, you can save one line here as follows:
MaybeObject* maybe_map =
    function->map()->CopyReplaceDescriptor(
        &new_desc, index, OMIT_TRANSITION);
but I don't feel strongly about it either way. Choose whatever you find is more
readable.

[Toon Verwaest, 2012-07-17 13:48:16]

Addressed comments.