Implementation of null-aware operators.

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

Index: pkg/compiler/lib/src/scanner/scanner.dart
diff --git a/pkg/compiler/lib/src/scanner/scanner.dart b/pkg/compiler/lib/src/scanner/scanner.dart
index 8a3880242bc6e7943b3053e65f5b10bf658b23cf..e330f14944ac921e0d3559667f9990e5b1cbdebd 100644
--- a/pkg/compiler/lib/src/scanner/scanner.dart
+++ b/pkg/compiler/lib/src/scanner/scanner.dart
@@ -330,8 +330,7 @@ abstract class AbstractScanner implements Scanner {
     }
 
     if (identical(next, $QUESTION)) {
-      appendPrecedenceToken(QUESTION_INFO);
-      return advance();
+      return tokenizeQuestion(next);
     }
 
     if (identical(next, $CLOSE_SQUARE_BRACKET)) {
@@ -450,6 +449,20 @@ abstract class AbstractScanner implements Scanner {
     return select($EQ, CARET_EQ_INFO, CARET_INFO);
   }
 
+  int tokenizeQuestion(int next) {
+    // ? ?. ?? ??=
+    next = advance();
+    if (identical(next, $QUESTION)) {
+      return select($EQ, QUESTION_QUESTION_EQ_INFO, QUESTION_QUESTION_INFO);
+    } else if (identical(next, $PERIOD)) {
+      appendPrecedenceToken(QUESTION_PERIOD_INFO);
+      return advance();
+    } else {
+      appendPrecedenceToken(QUESTION_INFO);
+      return next;
+    }
+  }
+
   int tokenizeBar(int next) {
     // | || |=
     next = advance();