The current implementation failed when comparing an integral type to a
reference to an integral type of different signedness (see updated
unittest).
This CL fixes the checks to actually test the std::decay<T>::type,
i.e. with all references, const or volatile modifiers stripped.

R=jochen@chromium.org, ishell@chromium.org
TEST=unittests/LoggingTest.CompareWithReferenceType

Change-Id: Ib0ac077a91e0409ada7a80b68150cb98cbdd32f1
Reviewed-on: https://chromium-review.googlesource.com/502814Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45271}