Implementation of null-aware operators.

pkg/compiler/lib/src/scanner/parser.dart

Index: pkg/compiler/lib/src/scanner/parser.dart
diff --git a/pkg/compiler/lib/src/scanner/parser.dart b/pkg/compiler/lib/src/scanner/parser.dart
index 9098587a45bef343bfbc5a39c7f27ebb076919a2..10e7dfc35d5ba61f592ce5a1705782f238316610 100644
--- a/pkg/compiler/lib/src/scanner/parser.dart
+++ b/pkg/compiler/lib/src/scanner/parser.dart
@@ -1784,7 +1784,8 @@ class Parser {
           token = parsePrecedenceExpression(token.next, level, allowCascades);
           listener.handleAssignmentExpression(operator);
         } else if (identical(tokenLevel, POSTFIX_PRECEDENCE)) {
-          if (identical(info, PERIOD_INFO)) {
+          if (identical(info, PERIOD_INFO) ||
+              identical(info, QUESTION_PERIOD_INFO)) {
             // Left associative, so we recurse at the next higher
             // precedence level. However, POSTFIX_PRECEDENCE is the
             // highest level, so we just call parseUnaryExpression