GN: Mark all variables used when defining a template.

This exempts file-scoped values from used variable checking when a template is
defined. This avoids spurious unused variable warnings at the expense of
potentially missing unused variables in some cases. These warnings have tripped
people up multiple times.

The potential for missing actual unused values is pretty small, however,
because most templates are defined in .gni files that don't have used variable
checking (since they could be included into many different contexts).

BUG=395883

Review-Url: https://codereview.chromium.org/2233893005
Cr-Original-Commit-Position: refs/heads/master@{#411265}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: ba1286d0e720ef723192e4a2af7e99d0516495d6
3 files changed
tree: 1c1da604a03d5e65fac92bafe35f29b7161995af
  1. tools/