Use inferred type in the SSA builder for super calls, and fix a bug with operator== in the type inf…

sdk/lib/_internal/compiler/implementation/types/simple_types_inferrer.dart

Index: sdk/lib/_internal/compiler/implementation/types/simple_types_inferrer.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/types/simple_types_inferrer.dart	(revision 20142)
+++ sdk/lib/_internal/compiler/implementation/types/simple_types_inferrer.dart	(working copy)
@@ -108,6 +108,8 @@
     throw 'Unsupported operation';
   }
 
+  bool get isNullable => true;
+
   String toString() => '$name sentinel type mask';
 }
 
@@ -1048,6 +1050,17 @@
         // also return null.
         returnType = returnType.nullable();
       }
+
+      if (analyzedElement.name == const SourceString('==')) {
+        // TODO(ngeoffray): Should this be done at the call site?
+        // When the argument passed in is null, we know we return a
+        // bool.
+        signature.forEachParameter((Element parameter) {
+          if (inferrer.typeOfElement(parameter).isNullable){
+            returnType = inferrer.computeLUB(returnType, inferrer.boolType);
+          }
+        });
+      }
     }
 
     if (analyzedElement == outermostElement) {