Add alias identity information to array allocations.

Add alias identity information to array allocations.

Loads/stores with non-escaping arrays can be disambiguated from loads/store
with unknown identity.

This enables better load elimination for non-escaping arrays.

For example in the following code:

test() {
  var a = new List(1);
  var b = new List(1);
  a[0] = 42;
  b[0] = 43;
  return a[0] + b[0];
}

we can now eliminate both loads a[0] and b[0] where before all stores to [0] were
considered to interfere with each other..

R=srdjan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=33523

[srdjan, 2014-03-10 22:20:37]

lgtm

[Florian Schneider, 2014-03-11 09:39:27]

Committed patchset #2 manually as r33523 (presubmit successful).