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 7957b5e929335a86fe54b2ecd214e6636d08c885..7a7a312bbddaf35816f01d59f047894b6373a703 100644
--- a/pkg/compiler/lib/src/scanner/parser.dart
+++ b/pkg/compiler/lib/src/scanner/parser.dart
@@ -1789,7 +1789,8 @@ 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