Stop defensively copying AST structures before resolution

pkg/analyzer/lib/src/task/dart.dart

Index: pkg/analyzer/lib/src/task/dart.dart
diff --git a/pkg/analyzer/lib/src/task/dart.dart b/pkg/analyzer/lib/src/task/dart.dart
index fb3c3c1f637b5cde0251cc07cedc08934baa362a..aa910b20e2ef1f130a78e96ece9ecb0b044ef503 100644
--- a/pkg/analyzer/lib/src/task/dart.dart
+++ b/pkg/analyzer/lib/src/task/dart.dart
@@ -537,7 +537,7 @@ class BuildCompilationUnitElementTask extends SourceBasedAnalysisTask {
     //
     // Build or reuse CompilationUnitElement.
     //
-    unit = AstCloner.clone(unit);
+//    unit = AstCloner.clone(unit);
     AnalysisCache analysisCache =
         (context as InternalAnalysisContext).analysisCache;
     CompilationUnitElement element =
@@ -573,7 +573,7 @@ class BuildCompilationUnitElementTask extends SourceBasedAnalysisTask {
   static Map<String, TaskInput> buildInputs(AnalysisTarget target) {
     LibrarySpecificUnit unit = target;
     return <String, TaskInput>{
-      PARSED_UNIT_INPUT_NAME: PARSED_UNIT.of(unit.unit)
+      PARSED_UNIT_INPUT_NAME: PARSED_UNIT.of(unit.unit, flushOnAccess: true)
     };
   }
 
@@ -4111,6 +4111,9 @@ class _SourceClosureTaskInputBuilder implements TaskInputBuilder<List<Source>> {
   }
 
   @override
+  bool get flushOnAccess => false;
+
+  @override
   List<Source> get inputValue {
     return _libraries.map((LibraryElement library) => library.source).toList();
   }