Ignore empty lines in print-mapping test.

R=sgjesse

Change-Id: Ib95aef20a3b7e4bfe2e519268c19dae4c459d4ee
diff --git a/src/test/java/com/android/tools/r8/shaking/TreeShakingSpecificTest.java b/src/test/java/com/android/tools/r8/shaking/TreeShakingSpecificTest.java
index 9b6ba29..94e2ca1 100644
--- a/src/test/java/com/android/tools/r8/shaking/TreeShakingSpecificTest.java
+++ b/src/test/java/com/android/tools/r8/shaking/TreeShakingSpecificTest.java
@@ -101,6 +101,6 @@
 
   private static String sorted(String str) {
     return new BufferedReader(new StringReader(str))
-        .lines().sorted().collect(Collectors.joining("\n"));
+        .lines().sorted().filter(s -> !s.isEmpty()).collect(Collectors.joining("\n"));
   }
 }