1) CSA::Select() receives lambdas for generating true/false values.
   The representation parameter made mandatory.
2) CSA::Select[Type]Constant() methods receive true/false nodes directly.
   These methods are intended to be used for generating "selects" when
   true/false values are already computed.

BUG=

Review-Url: https://codereview.chromium.org/2550683003
Cr-Commit-Position: refs/heads/master@{#41483}