dart2js cps: Insert refinements for identical(x, null) in condition.

pkg/compiler/lib/src/cps_ir/insert_refinements.dart

Index: pkg/compiler/lib/src/cps_ir/insert_refinements.dart
diff --git a/pkg/compiler/lib/src/cps_ir/insert_refinements.dart b/pkg/compiler/lib/src/cps_ir/insert_refinements.dart
index 5b6ce826aba97ffdbdef32d7df9812b43a726e6f..03cafdf3054ef89e8b366d65898f76eeffbcfc10 100644
--- a/pkg/compiler/lib/src/cps_ir/insert_refinements.dart
+++ b/pkg/compiler/lib/src/cps_ir/insert_refinements.dart
@@ -182,25 +182,46 @@ class InsertRefinements extends RecursiveVisitor implements Pass {
     }
 
     // If the condition is comparison with a constant, promote the other value.
-    if (call is InvokeMethod && call.selector == Selectors.equals) {
-      Primitive first = call.arguments[0].definition;
-      Primitive second = call.arguments[1].definition;
+    // This can happen either for calls to `==` or `identical` calls, such
+    // as the ones inserted by the unsugaring pass.
+
+    void refineEquality(Primitive first,
+                        Primitive second,
+                        Continuation trueCont,
+                        Continuation falseCont) {
       if (second is Constant && second.value.isNull) {
         Refinement refinedTrue = new Refinement(first, nullType);
         Refinement refinedFalse = new Refinement(first, nonNullType);
         pushRefinement(trueCont, refinedTrue);
         pushRefinement(falseCont, refinedFalse);
-        return;
-      }
-      if (first is Constant && first.value.isNull) {
+      } else if (first is Constant && first.value.isNull) {
         Refinement refinedTrue = new Refinement(second, nullType);
         Refinement refinedFalse = new Refinement(second, nonNullType);
         pushRefinement(trueCont, refinedTrue);
         pushRefinement(falseCont, refinedFalse);
-        return;
+      } else {
+        push(trueCont);
+        push(falseCont);
       }
     }
 
+    if (call is InvokeMethod && call.selector == Selectors.equals) {
+      refineEquality(call.arguments[0].definition,
+                     call.arguments[1].definition,
+                     trueCont,
+                     falseCont);
+      return;
+    }
+
+    if (condition is ApplyBuiltinOperator &&
+        condition.operator == BuiltinOperator.Identical) {
+      refineEquality(condition.arguments[0].definition,
+                     condition.arguments[1].definition,
+                     trueCont,
+                     falseCont);
+      return;
+    }
+
     push(trueCont);
     push(falseCont);
   }