Rename source_prereqs to inputs in the GN build.

This variable changed name.

R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/375873006

Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: a901cc9a31b96f16796290262cf248abb6432980
2 files changed