[PrintUses] Print method when assertion fails

This is helpful for debugging failing builds

Change-Id: Ica5999be959bc208c1cdd6e6baaed3dd9679b93d
diff --git a/src/main/java/com/android/tools/r8/PrintUses.java b/src/main/java/com/android/tools/r8/PrintUses.java
index 2864dfb..b906cb2 100644
--- a/src/main/java/com/android/tools/r8/PrintUses.java
+++ b/src/main/java/com/android/tools/r8/PrintUses.java
@@ -215,7 +215,7 @@
       Set<DexMethod> typeMethods = methods.get(method.holder);
       if (typeMethods != null) {
         DexEncodedMethod encodedMethod = appInfo.definitionFor(method);
-        assert encodedMethod != null;
+        assert encodedMethod != null : "Could not find method " + method.toString();
         if (!allowObfuscation) {
           noObfuscationTypes.add(method.holder);
         }