Add FunctionEntity.asyncMarker and refactor SourceInformationStrategy to avoid ResolvedAst

pkg/compiler/lib/src/elements/entities.dart

Index: pkg/compiler/lib/src/elements/entities.dart
diff --git a/pkg/compiler/lib/src/elements/entities.dart b/pkg/compiler/lib/src/elements/entities.dart
index eedc0f65841a37aa6dcbd78733b3c3603a58d257..c6b4bbbf188c02c38047f9486aee0da00b6cc446 100644
--- a/pkg/compiler/lib/src/elements/entities.dart
+++ b/pkg/compiler/lib/src/elements/entities.dart
@@ -4,6 +4,9 @@
 
 library entities;
 
+import 'package:front_end/src/fasta/parser/async_modifier.dart'
+    show AsyncModifier;
+
 import '../common.dart';
 import '../universe/call_structure.dart' show CallStructure;
 
@@ -123,6 +126,61 @@ abstract class FunctionEntity extends MemberEntity {
 
   /// The structure of the function parameters.
   ParameterStructure get parameterStructure;
+
+  /// The synchronous/asynchronous marker on this function.
+  AsyncMarker get asyncMarker;
+}
+
+/// Enum for the synchronous/asynchronous function body modifiers.
+class AsyncMarker {
+  /// The default function body marker.
+  static const AsyncMarker SYNC = const AsyncMarker._(AsyncModifier.Sync);
+
+  /// The `sync*` function body marker.
+  static const AsyncMarker SYNC_STAR =
+      const AsyncMarker._(AsyncModifier.SyncStar, isYielding: true);
+
+  /// The `async` function body marker.
+  static const AsyncMarker ASYNC =
+      const AsyncMarker._(AsyncModifier.Async, isAsync: true);
+
+  /// The `async*` function body marker.
+  static const AsyncMarker ASYNC_STAR = const AsyncMarker._(
+      AsyncModifier.AsyncStar,
+      isAsync: true,
+      isYielding: true);
+
+  /// Is `true` if this marker defines the function body to have an
+  /// asynchronous result, that is, either a [Future] or a [Stream].
+  final bool isAsync;
+
+  /// Is `true` if this marker defines the function body to have a plural
+  /// result, that is, either an [Iterable] or a [Stream].
+  final bool isYielding;
+
+  final AsyncModifier asyncParserState;
+
+  const AsyncMarker._(this.asyncParserState,
+      {this.isAsync: false, this.isYielding: false});
+
+  String toString() {
+    return '${isAsync ? 'async' : 'sync'}${isYielding ? '*' : ''}';
+  }
+
+  /// Canonical list of marker values.
+  ///
+  /// Added to make [AsyncMarker] enum-like.
+  static const List<AsyncMarker> values = const <AsyncMarker>[
+    SYNC,
+    SYNC_STAR,
+    ASYNC,
+    ASYNC_STAR
+  ];
+
+  /// Index to this marker within [values].
+  ///
+  /// Added to make [AsyncMarker] enum-like.
+  int get index => values.indexOf(this);
 }
 
 /// Stripped down super interface for constructor like entities.