Fix inputs for main_dex_list action.

build/config/android/internal_rules.gni

Index: build/config/android/internal_rules.gni
diff --git a/build/config/android/internal_rules.gni b/build/config/android/internal_rules.gni
index 4bc405dddcc2ec8342e7af827f087e25d0a0018c..46c3d55663775f3e16b9642e49f157ad31462dcd 100644
--- a/build/config/android/internal_rules.gni
+++ b/build/config/android/internal_rules.gni
@@ -925,6 +925,11 @@ if (enable_java_templates) {
 
         main_dex_rules = "//build/android/main_dex_classes.flags"
 
+        if (!defined(inputs)) {
+          inputs = []
+        }
+        inputs += [ main_dex_rules ]
+
         outputs = [
           _main_dex_list_path,
         ]