Minor updates to dataflow analysis framework

Change-Id: I0edd86b66d4dc8305ae8b40ad1feaaa05b4c2574
diff --git a/src/main/java/com/android/tools/r8/ir/code/BasicBlock.java b/src/main/java/com/android/tools/r8/ir/code/BasicBlock.java
index e81d765..7dbc0ad 100644
--- a/src/main/java/com/android/tools/r8/ir/code/BasicBlock.java
+++ b/src/main/java/com/android/tools/r8/ir/code/BasicBlock.java
@@ -190,6 +190,10 @@
     return successors.size() == 1;
   }
 
+  public boolean hasUniqueSuccessorWithUniquePredecessor() {
+    return hasUniqueSuccessor() && getUniqueSuccessor().getPredecessors().size() == 1;
+  }
+
   public boolean hasUniqueNormalSuccessor() {
     return numberOfNormalSuccessors() == 1;
   }