Start new design for interceptors and implement String.charCodeAt with it.

sdk/lib/_internal/compiler/implementation/ssa/nodes.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;
 
 abstract class HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBailoutTarget(HBailoutTarget node);
   R visitBitAnd(HBitAnd node);
@@ skipping 499 matching lines @@
     HInstruction instruction = first;
     while (instruction != null) {
       int instructionId = instruction.id;
       String inputsAsString = instruction.inputsToString();
       compiler.log('$instructionId: $instruction $inputsAsString');
       instruction = instruction.next;
     }
   }
 
   void addAtEntry(HInstruction instruction) {
-    assert(isClosed());
     assert(instruction is !HPhi);
     super.addBefore(first, instruction);
     instruction.notifyAddedToBlock(this);
   }
 
   void addAtExit(HInstruction instruction) {
     assert(isClosed());
     assert(last is HControlFlow);
     assert(instruction is !HPhi);
     super.addBefore(last, instruction);
@@ skipping 1621 matching lines @@
 }
 
 class HParameterValue extends HLocalValue {
   HParameterValue(Element element) : super(element);
 
   toString() => 'parameter ${sourceElement.name.slowToString()}';
   accept(HVisitor visitor) => visitor.visitParameterValue(this);
 }
 
 class HThis extends HParameterValue {
-  HThis([HType type = HType.UNKNOWN]) : super(null) {
+  HThis(Element element, [HType type = HType.UNKNOWN]) : super(element) {
     guaranteedType = type;
   }
   toString() => 'this';
   accept(HVisitor visitor) => visitor.visitThis(this);
 }
 
 class HPhi extends HInstruction {
   static const IS_NOT_LOGICAL_OPERATOR = 0;
   static const IS_AND = 1;
   static const IS_OR = 2;
@@ skipping 842 matching lines @@
   HBasicBlock get start => expression.start;
   HBasicBlock get end {
     // We don't create a switch block if there are no cases.
     assert(!statements.isEmpty);
     return statements.last.end;
   }
 
   bool accept(HStatementInformationVisitor visitor) =>
       visitor.visitSwitchInfo(this);
 }