Add assertion that ensures no hash change for CachedHashValueDexItem

Bug: 139991218
Change-Id: I8ab9167da35cd7ca3874178a9463182764c4cd90
diff --git a/src/main/java/com/android/tools/r8/graph/CachedHashValueDexItem.java b/src/main/java/com/android/tools/r8/graph/CachedHashValueDexItem.java
index 8f110d5..749ce04 100644
--- a/src/main/java/com/android/tools/r8/graph/CachedHashValueDexItem.java
+++ b/src/main/java/com/android/tools/r8/graph/CachedHashValueDexItem.java
@@ -26,6 +26,8 @@
       }
       hash = cache;
     }
+    assert cache == computeHashCode()
+        : "Hash code for " + this + " has changed from " + hash + " to " + computeHashCode();
     return cache;
   }