Revert r23380, some browser tests fail.

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 49 matching lines @@
           defaultValueTypes =
               new OptionalParameterTypes(signature.optionalParameterCount);
           int index = 0;
           signature.forEachOptionalParameter((Element parameter) {
             Constant defaultValue = builder.compileVariable(parameter);
             HType type = HGraph.mapConstantTypeToSsaType(defaultValue);
             defaultValueTypes.update(index, parameter.name, type);
             index++;
           });
         } else {
-          // BUG(10938): the types are stored in the wrong order.
+          // TODO(ahe): I have disabled type optimizations for
+          // optional arguments as the types are stored in the wrong
           // order.
           HTypeList parameterTypes =
               backend.optimisticParameterTypes(element.declaration,
                                                defaultValueTypes);
           if (!parameterTypes.allUnknown) {
             int i = 0;
             signature.forEachParameter((Element param) {
               builder.parameters[param].instructionType = parameterTypes[i++];
             });
           }
@@ skipping 5290 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;
   }
 }