dart2js: Keep refined type for type checks

pkg/compiler/lib/src/ssa/codegen_helpers.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import '../compiler.dart' show Compiler;
 import '../constants/values.dart';
 import '../elements/elements.dart';
 import '../js_backend/js_backend.dart';
 import '../types/types.dart';
 import '../universe/selector.dart' show Selector;
@@ skipping 265 matching lines @@
   void visitBasicBlock(HBasicBlock block) {
     HInstruction instruction = block.first;
     while (instruction != null) {
       HInstruction next = instruction.next;
       instruction.accept(this);
       instruction = next;
     }
   }
 
   void visitTypeKnown(HTypeKnown instruction) {
+    for (HInstruction user in instruction.usedBy) {
+      if (user is HTypeConversion) {
+        user.inputType = instruction.instructionType;
+      }
+    }
     instruction.block.rewrite(instruction, instruction.checkedInput);
     instruction.block.remove(instruction);
   }
 }
 
 /**
  * Remove [HTypeConversion] instructions from the graph in '--trust-primitives'
  * mode.
  */
 class SsaTrustedCheckRemover extends HBaseVisitor {
@@ skipping 501 matching lines @@
     }
 
     // If [thenInput] is defined in the first predecessor, then it is only used
     // by [phi] and can be generated at use site.
     if (identical(thenInput.block, end.predecessors[0])) {
       assert(thenInput.usedBy.length == 1);
       markAsGenerateAtUseSite(thenInput);
     }
   }
 }