Do not type check parameters that are not passed directly.

sdk/lib/_internal/compiler/implementation/ssa/builder.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.
 
 part of ssa;
 
 /**
  * A special element for the extra parameter taken by intercepted
  * methods. We need to override [Element.computeType] because our
  * optimizers may look at its declared type.
@@ skipping 1589 matching lines @@
       signature.orderedForEachParameter((Element parameterElement) {
         if (elements.isParameterChecked(parameterElement)) {
           addParameterCheckInstruction(parameterElement);
         }
       });
 
       // Put the type checks in the first successor of the entry,
       // because that is where the type guards will also be inserted.
       // This way we ensure that a type guard will dominate the type
       // check.
-      signature.orderedForEachParameter((Element element) {
+      signature.orderedForEachParameter((Element parameterElement) {
+        if (element.isGenerativeConstructorBody()) {
+          ClosureScope scopeData =
+              localsHandler.closureData.capturingScopes[node];
+          if (scopeData != null
+              && scopeData.capturedVariableMapping.containsKey(
+                  parameterElement)) {
+            // The parameter will be a field in the box passed as the
+            // last parameter. So no need to have it.
+            return;
+          }
+        }
         HInstruction newParameter = potentiallyCheckType(
-            localsHandler.directLocals[element],
-            element.computeType(compiler));
-        localsHandler.directLocals[element] = newParameter;
+            localsHandler.directLocals[parameterElement],
+            parameterElement.computeType(compiler));
+        localsHandler.directLocals[parameterElement] = newParameter;
       });
 
       returnType = signature.returnType;
     } else {
       // Otherwise it is a lazy initializer which does not have parameters.
       assert(element is VariableElement);
     }
 
     // Add the type parameters of the class as parameters of this
     // method.
@@ skipping 3346 matching lines @@
           new HSubGraphBlockInformation(elseBranch.graph));
 
     HBasicBlock conditionStartBlock = conditionBranch.block;
     conditionStartBlock.setBlockFlow(info, joinBlock);
     SubGraph conditionGraph = conditionBranch.graph;
     HIf branch = conditionGraph.end.last;
     assert(branch is HIf);
     branch.blockInformation = conditionStartBlock.blockFlow;
   }
 }