Do not build share_service_impl and associated test on Mac/Android.

These files are not used on those platforms and have a growing number of
conditional compilation statements which can be removed in a follow-up
CL.

BUG=668389

Review-Url: https://codereview.chromium.org/2695563002
Cr-Commit-Position: refs/heads/master@{#449905}
3 files changed