E.g. use TrueConstant() instead of BooleanConstant(true) and
NullConstant() instead of HeapConstant(factory...null_value()).

R=jkummerow@chromium.org

Bug: 
Change-Id: I0588d71940d8baf289eb8f8e6c8d20aa717d57f6
Reviewed-on: https://chromium-review.googlesource.com/735681
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48911}