Improve canonicalization of strict comparisons and bool negation.

Improve canonicalization of strict comparisons and bool negation.

This CL generalizes the existing optimization to handle all combinations

expr === true
expr !== true
expr === false
expr !== false

including lhs and rhs swapped. It also adds canonicalization of boolean
negation.

R=kmillikin@google.com

Committed: https://code.google.com/p/dart/source/detail?r=28802

[Kevin Millikin (Google), 2013-10-17 14:00:17]

lgtm

[Florian Schneider, 2013-10-17 14:01:08]

Committed patchset #1 manually as r28802 (presubmit successful).