Linux: change protobuf default option to allow building
with unpatched system protobuf.

This is a preparation for landing https://codereview.chromium.org/11231046/
and a solution chosen because our custom protobuf changes will not
be accepted upstream.

Setting defaults to optimize for lite runtime and retain unknown fields
makes it possible to use the same .proto files with system protobuf.

BUG=157155
TEST=none

Review URL: https://codereview.chromium.org/11228038

git-svn-id: http://src.chromium.org/svn/trunk/src/chrome/browser/policy/proto@166534 4ff67af0-8c30-449e-8e8b-ad334ec8d88c
4 files changed