Use Relationship as a first key in the index store.

Use Relationship as a first key in the index store.

This significantly speeds up computing type hierarchies.
For example for List we don't have to read all the nodes (files) where it is
used as a type annotation. We read node where it IS_EXTENDED_BY and IS_IMPLEMENTED_BY.

R=brianwilkerson@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=40152

[Brian Wilkerson, 2014-09-11 14:42:22]

LGTM

> This significantly speeds up computing type hierarchies.

Do you have any information about what it does for other queries?

[scheglov, 2014-09-11 15:40:55]

Committed patchset #1 (id:1) manually as 40152 (presubmit successful).

[scheglov, 2014-09-11 15:44:03]

On 2014/09/11 14:42:22, Brian Wilkerson wrote:
> LGTM
> 
> > This significantly speeds up computing type hierarchies.
> 
> Do you have any information about what it does for other queries?

It also significantly speeds up search for member references, because we
actually return all the references to all the member in the hierarchy.
So, for example when we search for String.endsWidth, we try to build String
hierarchy (only String) and it is the same index request as "Type Hierarchy"
does.
So, it is now also about 200 ms (with analyzer project only) vs. 2000+ ms
before.