Fix result cid of CompactLinkedHashMap._index native getter.

Fix result cid of CompactLinkedHashMap._index native getter.

This field can be null when a hash map is deserialized from a snapshot where
the index is regenerated.

BUG=
R=iposva@google.com, koda@google.com

Committed: https://github.com/dart-lang/sdk/commit/63209c93d3572926c42e748395ebc9f31dbce273

[Florian Schneider, 2015-06-03 14:59:05]

fschneider@google.com changed reviewers:
+ iposva@google.com, koda@google.com

[Ivan Posva, 2015-06-03 14:59:39]

LGTM!

-Ivan

[koda, 2015-06-03 15:00:51]

lgtm

[Florian Schneider, 2015-06-03 15:01:39]

Committed patchset #1 (id:1) manually as
63209c93d3572926c42e748395ebc9f31dbce273 (presubmit successful).

[koda, 2015-06-03 15:13:13]

Thanks for fixing this. In an earlier version, an empty index array was
allocated in the deserialization (and then populated in Dart). That would have
avoided this issue.

Is there a significant performance impact from having this as dynamic?

[Florian Schneider, 2015-06-04 08:39:23]

On 2015/06/03 15:13:13, koda wrote:
> Thanks for fixing this. In an earlier version, an empty index array was
> allocated in the deserialization (and then populated in Dart). That would have
> avoided this issue.
> 
> Is there a significant performance impact from having this as dynamic?

There is a check for null, but in case of using an empty array, there would be a
length-check instead, so I think the approach of using null is as good.