Implementation of null-aware operators.

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index 8046c5b9642602cbbee9dfb6e16ffa05e849ea80..65d269cb85c32d5bfd6c39cf2e3f5805f38b99a4 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -781,6 +781,10 @@ abstract class Compiler implements DiagnosticListener {
   /// If `true` native extension syntax is supported by the frontend.
   final bool allowNativeExtensions;
 
+  /// Temporary flag to enable `?.`, `??`, and `??=` until it becomes part of
+  /// the spec.
+  final bool enableNullAwareOperators;
+
   /// Output provider from user of Compiler API.
   api.CompilerOutputProvider userOutputProvider;
 
@@ -1044,6 +1048,7 @@ abstract class Compiler implements DiagnosticListener {
             bool hasIncrementalSupport: false,
             this.enableExperimentalMirrors: false,
             this.allowNativeExtensions: false,
+            this.enableNullAwareOperators: false,
             this.generateCodeWithCompileTimeErrors: false,
             api.CompilerOutputProvider outputProvider,
             List<String> strips: const []})