Verify that debug start and end point instructions are in the user set.

R=ager

Change-Id: Ia7a88482bd4a43c27966392ccd9f113fbbe6e8de
diff --git a/src/main/java/com/android/tools/r8/ir/code/IRCode.java b/src/main/java/com/android/tools/r8/ir/code/IRCode.java
index 21ed16e..c64d5d6 100644
--- a/src/main/java/com/android/tools/r8/ir/code/IRCode.java
+++ b/src/main/java/com/android/tools/r8/ir/code/IRCode.java
@@ -220,6 +220,12 @@
         assert verifyPhi(phiUser);
         assert phiUser.getDebugValues().contains(value);
       }
+      for (Instruction instruction : value.getDebugLocalStarts()) {
+        assert value.debugUsers().contains(instruction);
+      }
+      for (Instruction instruction : value.getDebugLocalEnds()) {
+        assert value.debugUsers().contains(instruction);
+      }
     }
     return true;
   }