[turbofan] Checking monotonicity of representation inference outputs and inputs.

src/compiler/representation-change.h

Index: src/compiler/representation-change.h
diff --git a/src/compiler/representation-change.h b/src/compiler/representation-change.h
index 5503b76cc4e94f2cab515baed20a21bd98e1c5bd..c26fdd3dcd62e3ccc28de6ed3a797664353e306b 100644
--- a/src/compiler/representation-change.h
+++ b/src/compiler/representation-change.h
@@ -46,6 +46,9 @@ class Truncation final {
 
   // Debug utilities.
   const char* description() const;
+  bool IsLessGeneralThan(Truncation other) {
+    return LessGeneral(kind(), other.kind());
+  }
 
  private:
   enum class TruncationKind : uint8_t {