Implement new constant expressions

editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/DartObjectImpl.java

Index: editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/DartObjectImpl.java
diff --git a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/DartObjectImpl.java b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/DartObjectImpl.java
index 7138576ce442331ca6f63de09feec9feb3409619..778fd9a0708c4ef01a52860d8db07b5190a6c4bf 100644
--- a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/DartObjectImpl.java
+++ b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/object/DartObjectImpl.java
@@ -64,6 +64,8 @@ public class DartObjectImpl implements DartObject {
       return new DartObjectImpl(typeProvider.getDoubleType(), result);
     } else if (result instanceof NumState) {
       return new DartObjectImpl(typeProvider.getNumType(), result);
+    } else if (result instanceof StringState) {
+      return new DartObjectImpl(typeProvider.getStringType(), result);
     }
     // We should never get here.
     throw new IllegalStateException("add returned a " + result.getClass().getName());
@@ -536,6 +538,17 @@ public class DartObjectImpl implements DartObject {
   }
 
   /**
+   * Return the result of invoking the 'length' getter on this object.
+   * 
+   * @param typeProvider the type provider used to find known types
+   * @return the result of invoking the 'length' getter on this object
+   * @throws EvaluationException if the operator is not appropriate for an object of this kind
+   */
+  public DartObjectImpl stringLength(TypeProvider typeProvider) throws EvaluationException {
+    return new DartObjectImpl(typeProvider.getIntType(), state.stringLength());
+  }
+
+  /**
    * Return the result of invoking the '*' operator on this object with the given argument.
    * 
    * @param typeProvider the type provider used to find known types