Fix incorrect assertion in vertical class merger

Change-Id: I9a5b79514c06fd9f66eccfb34956ad09173a7b57
diff --git a/src/main/java/com/android/tools/r8/shaking/VerticalClassMerger.java b/src/main/java/com/android/tools/r8/shaking/VerticalClassMerger.java
index b9ac49b..cf89715 100644
--- a/src/main/java/com/android/tools/r8/shaking/VerticalClassMerger.java
+++ b/src/main/java/com/android/tools/r8/shaking/VerticalClassMerger.java
@@ -697,7 +697,8 @@
           // can be mapped to the implementation method.
           DexMethod implementationMethod =
               ((SynthesizedBridgeCode) encodedMethod.getCode()).invocationTarget;
-          DexMethod originalImplementationMethod = graphLense.getOriginalMethodSignature(method);
+          DexMethod originalImplementationMethod =
+              graphLense.getOriginalMethodSignature(implementationMethod);
           assert originalMethod == originalImplementationMethod;
           assert implementationMethod == renamedMethod;
         } else {