Fix Windows client_tests GYP build after 88d8114fda3e

Bug: google-breakpad:770
Change-Id: I5539cda6053c39a11c354fba7f3e689ae02d3019
Reviewed-on: https://chromium-review.googlesource.com/1176126
Reviewed-by: Joshua Peraza <jperaza@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/src/client/windows/unittests/client_tests.gyp b/src/client/windows/unittests/client_tests.gyp
index b13603e..768f8fd 100644
--- a/src/client/windows/unittests/client_tests.gyp
+++ b/src/client/windows/unittests/client_tests.gyp
@@ -68,6 +68,7 @@
       'sources': [
         '<(DEPTH)/common/string_conversion.cc',
         '<(DEPTH)/processor/basic_code_modules.cc',
+        '<(DEPTH)/processor/convert_old_arm64_context.cc',
         '<(DEPTH)/processor/dump_context.cc',
         '<(DEPTH)/processor/dump_object.cc',
         '<(DEPTH)/processor/logging.cc',