[absl] Make 'testing' import chromium-only

Guard the 'testing' import (and therefore all tests) behind
build_with_chromium, so that projects using the chromium absl build
(e.g. V8) don't have to add a dependency on 'testing'.

Change-Id: Ie4427fe1aebddd14a0c773fa1bc5938e56d6d193
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2461312
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815552}

third_party/abseil-cpp/BUILD.gn

@@ -10,7 +10,6 @@ import("//build/config/c++/c++.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/toolchain.gni")
 import("//build_overrides/build.gni")
-import("//testing/test.gni")
 import("//third_party/abseil-cpp/absl.gni")
 
 config("absl_component_build") {
@@ -178,7 +177,10 @@ config("absl_test_cflags_cc") {
   }
 }
 
-if (!is_component_build) {
+if (build_with_chromium) {
+  import("//testing/test.gni")
+
+  if (!is_component_build) {
     test("absl_tests") {
       testonly = true
       deps = [
@@ -197,9 +199,8 @@ if (!is_component_build) {
         "//third_party/googletest:gtest_main",
       ]
     }
-}
+  }
 
-if (build_with_chromium) {
   test("absl_hardening_tests") {
     testonly = true
     sources = [ "absl_hardening_test.cc" ]