When clearing a field make the field state "does not exist"

This does not change the fact that the default value is returned when the field is cleared.

Tests for this in the dart-protoc-plugin package.

R=sigmund@google.com
BUG=#17

Review URL: https://chromiumcodereview.appspot.com//106663007

lib/generated_message.dart

@@ -874,18 +874,6 @@ abstract class GeneratedMessage {
 
   void clearField(int tagNumber) {
     _fieldValues.remove(tagNumber);
-    // Restore the default value for the field.
-    // For repeated fields, the default is an empty list.
-    // For required/optional fields, the BuilderInfo contains the initializer.
-    int fieldType = _getFieldType(tagNumber);
-    if ((fieldType & _REPEATED_BIT) != 0) {
-      _fieldValues[tagNumber] = new PbList();
-    } else {
-      var defaultValue = info_.defaultValue(tagNumber);
-      if (defaultValue != null) {
-        _fieldValues[tagNumber] = defaultValue;
-      }
-    }
   }
 
   bool extensionsAreInitialized() {

pubspec.yaml

@@ -1,5 +1,5 @@
 name: protobuf
-version: 0.3.2
+version: 0.3.3
 authors:
 - Dart Team <misc@dartlang.org>
 description: Runtime library for protobuf support.