Fix for issue 3401: Implement casts in Analyzer

compiler/java/com/google/dart/compiler/type/TypeAnalyzer.java

Index: compiler/java/com/google/dart/compiler/type/TypeAnalyzer.java
===================================================================
--- compiler/java/com/google/dart/compiler/type/TypeAnalyzer.java	(revision 8336)
+++ compiler/java/com/google/dart/compiler/type/TypeAnalyzer.java	(working copy)
@@ -424,6 +424,9 @@
          nonVoidTypeOf(rhsNode);
          return boolType;
 
+       case AS:
+         return typeOf(rhsNode);
+
        case IS:
          if (rhsNode instanceof DartUnaryExpression) {
            assert ((DartUnaryExpression) rhsNode).getOperator() == Token.NOT;
@@ -525,14 +528,14 @@
             @Override
             public Void visitBinaryExpression(DartBinaryExpression node) {
               // don't infer type if condition negated
-              if (!negation && node.getOperator() == Token.IS) {
+              if (!negation && (node.getOperator() == Token.IS || node.getOperator() == Token.AS)) {
                 DartExpression arg1 = node.getArg1();
                 DartExpression arg2 = node.getArg2();
                 if (arg1 instanceof DartIdentifier && arg1.getElement() instanceof VariableElement
                     && arg2 instanceof DartTypeExpression) {
                   VariableElement variableElement = (VariableElement) arg1.getElement();
-                  Type isType = arg2.getType();
-                  Type varType = Types.makeInferred(isType);
+                  Type rhsType = arg2.getType();
+                  Type varType = Types.makeInferred(rhsType);
                   variableRestorer.setType(variableElement, varType);
                 }
               }