VM: Materialize stub pc-markers (smi 0) eagerly on deoptimization.

VM: Materialize stub pc-markers (smi 0) eagerly on deoptimization.

Deferred objects are malloced, and there is no need to allocate one
for the stub pc-marker (smi zero).

This is also part of preparing for running precompiled stub code: when
changing the pc-marker to hold the stub's code object, we want to materialize
it eagerly, so that the stack frame is valid after DeoptimizeFillFrame.

BUG=
R=rmacnak@google.com

Committed: https://github.com/dart-lang/sdk/commit/fee8daa5c58dda650df5166b6e549356d3d94161

[Florian Schneider, 2015-08-14 11:15:03]

fschneider@google.com changed reviewers:
+ rmacnak@google.com

[rmacnak, 2015-08-14 20:22:45]

lgtm

[Florian Schneider, 2015-08-17 07:57:16]

Committed patchset #1 (id:1) manually as
fee8daa5c58dda650df5166b6e549356d3d94161 (presubmit successful).