A possible (non)solution would be to include the two components outside of build (grit and closure_compiler) as deps in v8. It'd make gn happy, but also download two unused repos on all v8 bots and dev machines.

I'd prefer making imports to things outside of //build conditional, being off by default in subprojects like v8, skia, pdfium, etc.

Adding a check to see if enable_resource_whitelist_generation is set instead of importing from //tools is another possible solution: https://codereview.chromium.org/2288273002/ 

Re 3: Even better!

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/47f910a6e58b633bd902adce24feecf26901f84d

commit 47f910a6e58b633bd902adce24feecf26901f84d
Author: estevenson <estevenson@chromium.org>
Date: Tue Aug 30 04:46:07 2016

Fix imports in gcc_toolchain.gni to not rely on //tools.

Importing //tools into gcc_toolchain.gni breaks certain downstream
projects that include //build but not //tools. This CL changes
gcc_toolchain.gni to only rely on files within //build.

BUG= 641981 

Review-Url: https://codereview.chromium.org/2288273002
Cr-Commit-Position: refs/heads/master@{#415113}

[modify] https://crrev.com/47f910a6e58b633bd902adce24feecf26901f84d/build/config/android/config.gni
[modify] https://crrev.com/47f910a6e58b633bd902adce24feecf26901f84d/build/toolchain/gcc_toolchain.gni
[modify] https://crrev.com/47f910a6e58b633bd902adce24feecf26901f84d/chrome/chrome_repack_locales.gni
[modify] https://crrev.com/47f910a6e58b633bd902adce24feecf26901f84d/tools/grit/grit_rule.gni

Thanks for fixing!