Add a hard dependency flag to the protobuf generation.
Add a hard dependency flag to the protobuf generation.

This was causing a build failure on the official builder, as without this flag Ninja assumes a link-time rather than a compile-time dependency.

BUG=
R=sebmarchand@chromium.org

Review URL: https://codereview.appspot.com/218930043

ericmckean/syzygy,wangming28/syzygy,supriyantomaftuh/syzygy,wangming28/syzygy,sebmarchand/syzygy,sebmarchand/syzygy,ericmckean/syzygy,google/syzygy,ericmckean/syzygy,Eloston/syzygy,supriyantomaftuh/syzygy,sebmarchand/syzygy,google/syzygy,sebmarchand/syzygy,ericmckean/syzygy,wangming28/syzygy,sebmarchand/syzygy,google/syzygy,wangming28/syzygy,Eloston/syzygy,supriyantomaftuh/syzygy,supriyantomaftuh/syzygy,google/syzygy,ericmckean/syzygy