Remove flag for enabling null-aware operators. They are now on by default.

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 65db47ebbbd0a91bd8e9c5266e57c5d5ad18479f..d9ab3123aa52e67f42569b3cff92ab92bb2bd7fb 100644
--- a/pkg/compiler/lib/src/scanner/scanner.dart
+++ b/pkg/compiler/lib/src/scanner/scanner.dart
@@ -8,13 +8,11 @@ abstract class Scanner {
   Token tokenize();
 
   factory Scanner(SourceFile file,
-      {bool includeComments: false, bool enableNullAwareOperators: false}) {
+      {bool includeComments: false}) {
     if (file is Utf8BytesSourceFile) {
-      return new Utf8BytesScanner(file, includeComments: includeComments,
-          enableNullAwareOperators: enableNullAwareOperators);
+      return new Utf8BytesScanner(file, includeComments: includeComments);
     } else {
-      return new StringScanner(file, includeComments: includeComments,
-          enableNullAwareOperators: enableNullAwareOperators);
+      return new StringScanner(file, includeComments: includeComments);
     }
   }
 }
@@ -23,7 +21,6 @@ abstract class AbstractScanner implements Scanner {
   // TODO(ahe): Move this class to implementation.
 
   final bool includeComments;
-  final bool enableNullAwareOperators;
 
   /**
    * The string offset for the next token that will be created.
@@ -58,7 +55,7 @@ abstract class AbstractScanner implements Scanner {
   final List<int> lineStarts = <int>[0];
 
   AbstractScanner(
-      this.file, this.includeComments, this.enableNullAwareOperators) {
+      this.file, this.includeComments) {
     this.tail = this.tokens;
   }
 
@@ -458,27 +455,9 @@ abstract class AbstractScanner implements Scanner {
     // ? ?. ?? ??=
     next = advance();
     if (identical(next, $QUESTION)) {
-      if (enableNullAwareOperators) {
-        return select($EQ, QUESTION_QUESTION_EQ_INFO, QUESTION_QUESTION_INFO);
-      } else {
-        next = advance();
-        PrecedenceInfo info;
-        if (identical(next, $EQ)) {
-          info = QUESTION_QUESTION_EQ_INFO;
-          next = advance();
-        } else {
-          info = QUESTION_QUESTION_INFO;
-        }
-        appendErrorToken(new UnsupportedNullAwareToken(info.value, tokenStart));
-        return next;
-      }
+      return select($EQ, QUESTION_QUESTION_EQ_INFO, QUESTION_QUESTION_INFO);
     } else if (identical(next, $PERIOD)) {
-      if (enableNullAwareOperators) {
-        appendPrecedenceToken(QUESTION_PERIOD_INFO);
-      } else {
-        appendErrorToken(new UnsupportedNullAwareToken(
-            QUESTION_PERIOD_INFO.value, tokenStart));
-      }
+      appendPrecedenceToken(QUESTION_PERIOD_INFO);
       return advance();
     } else {
       appendPrecedenceToken(QUESTION_INFO);