Switch dominator algorithm from [1] to [2].

Switch dominator algorithm from [1] to [2].

[1] has worse upper bound complexity than [2] but has lower
overhead. With [1] dart2js heaps would converge in ~10 iterations, but
with analyzer heaps would take ~10k iterations.

This reduces the time to analyze the final heap of the analyzer
analyzing dart2js from ~30 minutes to 26 seconds.

Increases peak memory usage by 21N bytes plus O(2N) words.

[1] "A Simple, Fast Dominance Algorithm." Keith D. Cooper, Timothy
J. Harvey, and Ken Kennedy.
[2] "A Fast Algorithm for Finding Dominators in a Flowgraph."
T. Lengauer and R. E. Tarjan.

R=johnmccutchan@google.com

Committed: https://github.com/dart-lang/sdk/commit/5eb3bccaf1f61e2993b8909a27a9256b96cb8e88

[rmacnak, 2015-11-17 00:42:36]

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

[Cutch, 2015-11-17 18:40:09]

LGTM after removing the two completely commented out functions.

https://codereview.chromium.org/1449243002/diff/1/runtime/observatory/lib/obj...
File runtime/observatory/lib/object_graph.dart (right):

https://codereview.chromium.org/1449243002/diff/1/runtime/observatory/lib/obj...
runtime/observatory/lib/object_graph.dart:648: // }
Remove commented out code.

[rmacnak, 2015-11-17 19:20:24]

https://codereview.chromium.org/1449243002/diff/1/runtime/observatory/lib/obj...
File runtime/observatory/lib/object_graph.dart (right):

https://codereview.chromium.org/1449243002/diff/1/runtime/observatory/lib/obj...
runtime/observatory/lib/object_graph.dart:648: // }
On 2015/11/17 18:40:09, Cutch wrote:
> Remove commented out code.

Done.

[rmacnak, 2015-11-17 19:20:42]

Committed patchset #1 (id:1) manually as
5eb3bccaf1f61e2993b8909a27a9256b96cb8e88 (presubmit successful).