Fix type warnings and a few other warnings, and probably even an error.

lib/compiler/implementation/typechecker.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.
 
 class TypeCheckerTask extends CompilerTask {
   TypeCheckerTask(Compiler compiler) : super(compiler);
   String get name() => "Type checker";
 
   static final bool LOG_FAILURES = false;
 
@@ skipping 259 matching lines @@
   }
 
   checkCondition(Expression condition) {
     checkAssignable(condition, boolType, analyze(condition));
   }
 
   void pushCascadeType(Type type) {
     cascadeTypes = cascadeTypes.prepend(type);
   }
 
-  void popCascadeType() {
+  Type popCascadeType() {
     Type type = cascadeTypes.head;
     cascadeTypes = cascadeTypes.tail;
     return type;
   }
 
   Type visitBlock(Block node) {
     return analyze(node.statements);
   }
 
   Type visitCascade(Cascade node) {
@@ skipping 458 matching lines @@
   }
 
   visitCatchBlock(CatchBlock node) {
     fail(node);
   }
 
   visitTypedef(Typedef node) {
     fail(node);
   }
 }