gn check will verify that dependencies are correctly described and not violated. For perfetto the dependency from unit tests to gtest seems wrong. (primiano said: "I think we need to tweak the part behind build_with_chromium")

To reproduce
-------------
(note that third_party/perfetto is not in .gn's check_targets list so not checked by default)
1. gn out/Default "//third_party/perfetto/*"

Expected
-----------
No errors

Actually
----------
About 10 of the error below:

ERROR at //third_party/perfetto/src/base/string_utils_unittest.cc:19:11: Can't include this header from here.
#include "gmock/gmock.h"
 ^------------
The target:
 //third_party/perfetto/src/base:unittests
is including a file from the target:
 //third_party/googletest:gmock

It's usually best to depend directly on the destination target.
In some cases, the destination target is considered a subcomponent
of an intermediate target. In this case, the intermediate target
should depend publicly on the destination to forward the ability
to include headers.

Dependency chain (there may also be others):
 //third_party/perfetto/src/base:unittests -->
 //third_party/perfetto/gn:gtest_deps -->
 //testing/gmock:gmock --[private]-->
 //third_party/googletest:gmock