Move cacheinvalidation testing file to a testing build target

This allows third_party/cache_invalidation to be checked
with gn check (as soon as it's enabled in //.gn).

Bug: 898837
Change-Id: Ica669d8a7277178878d630b54879e1439350f566
Reviewed-on: https://chromium-review.googlesource.com/c/1307496Reviewed-by: Nicolas Zea <zea@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#604196}

third_party/cacheinvalidation/BUILD.gn

@@ -14,8 +14,6 @@ config("cacheinvalidation_config") {
 static_library("cacheinvalidation") {
   sources = [
     "overrides/google/cacheinvalidation/deps/callback.h",
-    "overrides/google/cacheinvalidation/deps/gmock.h",
-    "overrides/google/cacheinvalidation/deps/googletest.h",
     "overrides/google/cacheinvalidation/deps/logging.h",
     "overrides/google/cacheinvalidation/deps/mutex.h",
     "overrides/google/cacheinvalidation/deps/random.cc",
@@ -92,6 +90,8 @@ static_library("cacheinvalidation") {
 
 test("cacheinvalidation_unittests") {
   sources = [
+    "overrides/google/cacheinvalidation/deps/gmock.h",
+    "overrides/google/cacheinvalidation/deps/googletest.h",
     "src/google/cacheinvalidation/impl/invalidation-client-impl_test.cc",
     "src/google/cacheinvalidation/impl/protocol-handler_test.cc",
     "src/google/cacheinvalidation/impl/recurring-task_test.cc",