[AiS] Update GN build, as well.

Previous CL for adding base_search_provider_unittest.cc did not update
BUILD.gn - this CL does.

BUG=none
TBR=mpearson@chromium.org

Review URL: https://codereview.chromium.org/600963002

Cr-Commit-Position: refs/heads/master@{#296538}

components/omnibox/BUILD.gn

@@ -71,6 +71,7 @@ source_set("unit_tests") {
     "autocomplete_input_unittest.cc",
     "autocomplete_match_unittest.cc",
     "autocomplete_result_unittest.cc",
+    "base_search_provider_unittest.cc",
     "keyword_provider_unittest.cc",
     "omnibox_field_trial_unittest.cc",
   ]
@@ -78,6 +79,7 @@ source_set("unit_tests") {
   deps = [
     ":omnibox",
     ":test_support",
+    "//testing/gmock",
     "//testing/gtest",
   ]
 }