[gn] Add extra library files in stand-alone mode.

BUG=chromium:474921
TBR=vogelheim@chromium.org, jochen@chromium.org
NOTRY=true

Review-Url: https://codereview.chromium.org/2046683003
Cr-Commit-Position: refs/heads/master@{#36777}

build_overrides/v8.gni

@@ -21,5 +21,7 @@ if (((v8_target_arch == "ia32" ||
 icu_use_data_file = false
 v8_imminent_deprecation_warnings = true
 v8_optimized_debug = false
-v8_extra_library_files = []
-v8_experimental_extra_library_files = []
+
+# Add simple extras solely for the purpose of the cctests.
+v8_extra_library_files = [ "//test/cctest/test-extra.js" ]
+v8_experimental_extra_library_files = [ "//test/cctest/test-experimental-extra.js" ]