Exclude new file in Google3 build.

The new file was added in https://codereview.chromium.org/1817633002

Review URL: https://codereview.chromium.org/1823703002
diff --git a/public.bzl b/public.bzl
index edd6947..5729be8 100644
--- a/public.bzl
+++ b/public.bzl
@@ -160,6 +160,7 @@
         "src/ports/SkFontConfigInterface_direct_factory.cpp",
         "src/ports/SkFontMgr_custom_directory_factory.cpp",
         "src/ports/SkFontMgr_custom_embedded_factory.cpp",
+        "src/ports/SkFontMgr_custom_empty_factory.cpp",
         "src/ports/SkFontMgr_empty_factory.cpp",
         "src/ports/SkFontMgr_fontconfig.cpp",
         "src/ports/SkFontMgr_fontconfig_factory.cpp",
@@ -208,6 +209,7 @@
         "src/ports/SkFontConfigInterface_direct_google3_factory.cpp",
         "src/ports/SkFontMgr_custom_directory_factory.cpp",
         "src/ports/SkFontMgr_custom_embedded_factory.cpp",
+        "src/ports/SkFontMgr_custom_empty_factory.cpp",
         "src/ports/SkFontMgr_empty_factory.cpp",
         "src/ports/SkImageDecoder_empty.cpp",
         "src/ports/SkImageGenerator_none.cpp",
@@ -263,6 +265,7 @@
         "src/ports/SkFontConfigInterface_direct_google3_factory.cpp",
         "src/ports/SkFontMgr_custom_directory_factory.cpp",
         "src/ports/SkFontMgr_custom_embedded_factory.cpp",
+        "src/ports/SkFontMgr_custom_empty_factory.cpp",
         "src/ports/SkFontMgr_empty_factory.cpp",
         "src/ports/SkImageGenerator_none.cpp",
         "src/ports/SkTLS_none.cpp",