dart2js cps: Do GVN for all primitives except fast constants.
dart2js cps: Do GVN for all primitives except fast constants.

Previously, trivial primitives such as "x+1" would not be hoisted.
Only fast constants are considered trivial now.

This is mainly to enable other optimizations.

BUG=
R=kmillikin@google.com

Review URL: https://codereview.chromium.org/1573473003 .

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