[turbofan] Optimize certain chains of Branch into a Switch.

test/unittests/compiler/graph-unittest.h

Index: test/unittests/compiler/graph-unittest.h
diff --git a/test/unittests/compiler/graph-unittest.h b/test/unittests/compiler/graph-unittest.h
index af07c93a75c6d4b5b02410f4769fe2b1ee899691..21f8ebf6b494be7f57facc86c6830d04f7397018 100644
--- a/test/unittests/compiler/graph-unittest.h
+++ b/test/unittests/compiler/graph-unittest.h
@@ -33,6 +33,8 @@ class GraphTest : public TestWithContext, public TestWithIsolateAndZone {
 
  protected:
   Node* start() { return graph()->start(); }
+  Node* end() { return graph()->end(); }
+
   Node* Parameter(int32_t index = 0);
   Node* Float32Constant(volatile float value);
   Node* Float64Constant(volatile double value);