tools/gn: mark first TestTarget parameter as const

Style guide mandates that parameters passed by reference must be labeled
'const'. That, or they should be const T*.

https://google.github.io/styleguide/cppguide.html#Reference_Arguments

This is also to please cpplint complain on it:
./tools/gn/test_with_scope.h:104:  Is this a non-const reference? If so,
make const or use a pointer: TestWithScope& setup [runtime/references] [2]

BUG=None
TEST=gn_unittests
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/1453843003

Cr-Original-Commit-Position: refs/heads/master@{#360251}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 45e4d2956883c02a20e0269ae74b24923a34cbc5
3 files changed
tree: bb3c5c4b5a78665acba5ba8fa9c7cc82e0f9a6e5
  1. tools/