Improve dead code analysis

[stevemessick]

The editor is able to detect that anything after the || in an expression such as "true || somethingElse" is dead code, but not in the case of "somethingElse || true." Not terribly important, perhaps, but an interesting failure to detect that case.
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Editor: 0.6.15_r25822 (2013-08-06)
OS: Linux - amd64 (3.2.5-gg1236)
JVM: 1.7.0-google-v5

projects: 5

open dart files: 21

auto-run pub: false
localhost resolves to: 127.0.0.1
mem max/total/free: 1778 / 1343 / 527 MB
thread count: 47
index: 1067880 relationships in 227842 keys in 1788 sources

SDK installed: true
Dartium installed: true
analysis engine: new

[bwilkerson]

Set owner to @jwren.
Removed Type-Defect label.
Added Type-Enhancement label.

[jwren]

The original code had this implemented, but it was commented out. See DeadCodeVerifier.visitBinaryExpression. The reason that it was removed was because the "true" part of "somethingElse || true" is not dead code, it will be executed. That said, it is pointless code, ... but not dead code.

If this inconsistency nags users we can always change it back for consistency.

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Added AsDesigned label.