Fix append_fallback_font_families_for_locale.

The language was being set to garbage, now set to part of the file name.
Add a test to ensure we continue to parse fallback directories correctly.

BUG=chromium:422180

Review URL: https://codereview.chromium.org/912053003
diff --git a/src/ports/SkFontConfigParser_android.h b/src/ports/SkFontConfigParser_android.h
index d77ca15..2302c77 100644
--- a/src/ports/SkFontConfigParser_android.h
+++ b/src/ports/SkFontConfigParser_android.h
@@ -101,7 +101,8 @@
 void GetCustomFontFamilies(SkTDArray<FontFamily*>& fontFamilies,
                            const SkString& basePath,
                            const char* fontsXml,
-                           const char* fallbackFontsXml);
+                           const char* fallbackFontsXml,
+                           const char* langFallbackFontsDir = NULL);
 
 } // SkFontConfigParser namespace