Set an empty classfile consumer in the main-dex tracing tool.

This ensures that the IR building has a specific output it is building
towards. The choice of CF or DEX is of little consequence.

Change-Id: Ib7db900c4db6ae7326b08d9edb9a86abe95dcba1
diff --git a/src/main/java/com/android/tools/r8/GenerateMainDexListCommand.java b/src/main/java/com/android/tools/r8/GenerateMainDexListCommand.java
index a79167a..f6a10a9 100644
--- a/src/main/java/com/android/tools/r8/GenerateMainDexListCommand.java
+++ b/src/main/java/com/android/tools/r8/GenerateMainDexListCommand.java
@@ -223,6 +223,7 @@
   @Override
   InternalOptions getInternalOptions() {
     InternalOptions internal = new InternalOptions(factory, reporter);
+    internal.programConsumer = ClassFileConsumer.emptyConsumer();
     internal.mainDexKeepRules = mainDexKeepRules;
     internal.mainDexListConsumer = mainDexListConsumer;
     internal.mainDexKeptGraphConsumer = mainDexKeptGraphConsumer;