Add monomorphic CompareNilICs and Crankshaft support

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index bd1dd403a79cbd397b2a9c56a48a590c71443216..6762ee3146e5b9c1284382ed76ddc1c6fe7f1409 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -3934,6 +3934,10 @@ class HCompareObjectEqAndBranch: public HTemplateControlInstruction<2, 2> {
     return Representation::Tagged();
   }
 
+  virtual Representation observed_input_representation(int index) {
+    return Representation::Tagged();
+  }
+
   DECLARE_CONCRETE_INSTRUCTION(CompareObjectEqAndBranch)
 };