Support native extensions for analysis and docgen.

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 fad4298d35af97a8d80cc6d5b4c10ba27292c562..07a9f0facb48071e53c628c1930f6d4c6a817356 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -725,6 +725,9 @@ abstract class Compiler implements DiagnosticListener {
   /// Incremental compilation is basically calling [run] more than once.
   final bool hasIncrementalSupport;
 
+  /// If `true` native extension syntax is supported by the frontend.
+  final bool allowNativeExtensions;
+
   api.CompilerOutputProvider outputProvider;
 
   bool disableInlining = false;
@@ -965,6 +968,7 @@ abstract class Compiler implements DiagnosticListener {
             this.suppressWarnings: false,
             bool hasIncrementalSupport: false,
             this.enableAsyncAwait: false,
+            this.allowNativeExtensions: false,
             api.CompilerOutputProvider outputProvider,
             List<String> strips: const []})
       : this.disableTypeInferenceFlag =
@@ -1901,6 +1905,7 @@ abstract class Compiler implements DiagnosticListener {
 
   void reportUnusedCode() {
     void checkLive(member) {
+      if (member.isErroneous) return;
       if (member.isFunction) {
         if (!enqueuer.resolution.hasBeenResolved(member)) {
           reportHint(member, MessageKind.UNUSED_METHOD,