Allow overriding Chromium-branded Android resources.

chrome/android/BUILD.gn

Index: chrome/android/BUILD.gn
diff --git a/chrome/android/BUILD.gn b/chrome/android/BUILD.gn
index b0cbbe1d64a7580ffd35c18dbca4ec2b98c2da40..f4558b7a021a98708971983086c4c0c8269ea3db 100644
--- a/chrome/android/BUILD.gn
+++ b/chrome/android/BUILD.gn
@@ -43,10 +43,10 @@ locale_pak_resources("chrome_locale_paks") {
 
 # GYP: //chrome/chrome.gyp:chrome_java (resources part)
 android_resources("chrome_java_resources") {
-  resource_dirs = [
-    "java/res",
-    "java/res_default",
-  ]
+  if (!defined(android_branding_res_dirs)) {
+    android_branding_res_dirs = [ "//chrome/android/java/res_chromium" ]
+  }
+  resource_dirs = [ "java/res" ] + android_branding_res_dirs
   deps = [
     ":chrome_locale_paks",
     ":chrome_strings_grd",