GitLab

Due to GetResolveParameterType(), the template was specialized for all
the cases used. Adding CdmPromiseTraits so that the specializations
are not needed, and the type set in the constructor appropriately.

BUG=358271
TEST=existing EME tests still pass

Review URL: https://codereview.chromium.org/567123002

Cr-Commit-Position: refs/heads/master@{#296112}