Move validation to validate.dart and add comments.

sdk/lib/_internal/compiler/implementation/ssa/codegen.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;
 
 class SsaCodeGeneratorTask extends CompilerTask {
 
   final JavaScriptBackend backend;
 
@@ skipping 737 matching lines @@
       currentBlockInformation = oldInfo;
     } else {
       generateStatements(info.body);
     }
   }
 
   bool visitLoopInfo(HLoopBlockInformation info) {
     HExpressionInformation condition = info.condition;
     bool isConditionExpression = isJSCondition(condition);
 
-    // Assert that the block we inserted to avoid critical edges satisfies
-    // basic assumptions.
-    assert(!condition.end.successors.last.isEmpty);
-    assert(condition.end.successors.last.first is HGoto);
-    assert(condition.end.successors.last.first.next == null);
-
     js.Loop loop;
 
     switch (info.kind) {
       // Treate all three "test-first" loops the same way.
       case HLoopBlockInformation.FOR_LOOP:
       case HLoopBlockInformation.WHILE_LOOP:
       case HLoopBlockInformation.FOR_IN_LOOP:
       case HLoopBlockInformation.SWITCH_CONTINUE_LOOP:
         HBlockInformation initialization = info.initializer;
         int initializationType = TYPE_STATEMENT;
@@ skipping 1943 matching lines @@
   js.PropertyAccess accessHelper(String name) {
     Element helper = compiler.findHelper(name);
     if (helper == null) {
       // For mocked-up tests.
       return js.js('(void 0).$name');
     }
     registry.registerStaticUse(helper);
     return backend.namer.elementAccess(helper);
   }
 }