Revert "Revert "Build new IR for functions returning a constant.""

sdk/lib/_internal/compiler/implementation/source_map_builder.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library source_map_builder;
 
 
 import 'util/util.dart';
 import 'scanner/scannerlib.dart' show Token;
 import 'source_file.dart';
@@ skipping 155 matching lines @@
   }
 }
 
 class SourceMapEntry {
   SourceFileLocation sourceLocation;
   int targetOffset;
 
   SourceMapEntry(this.sourceLocation, this.targetOffset);
 }
 
-class SourceFileLocation {
+abstract class SourceFileLocation {
   SourceFile sourceFile;
-  Token token;
+
+  SourceFileLocation(this.sourceFile) {
+    assert(isValid());
+  }
+
   int line;
 
-  SourceFileLocation(this.sourceFile, this.token) {
-    assert(isValid());
-  }
+  int get offset;
 
   String getSourceUrl() => sourceFile.filename;
 
   int getLine() {
-    if (line == null) line = sourceFile.getLine(token.charOffset);
+    if (line == null) line = sourceFile.getLine(offset);
     return line;
   }
 
-  int getColumn() => sourceFile.getColumn(getLine(), token.charOffset);
+  int getColumn() => sourceFile.getColumn(getLine(), offset);
+
+  String getSourceName();
+
+  bool isValid() => offset < sourceFile.length;
+}
+
+class TokenSourceFileLocation extends SourceFileLocation {
+  final Token token;
+
+  TokenSourceFileLocation(SourceFile sourceFile, this.token)
+    : super(sourceFile);
+
+  int get offset => token.charOffset;
 
   String getSourceName() {
     if (token.isIdentifier()) return token.value;
     return null;
   }
+}
 
-  bool isValid() => token.charOffset < sourceFile.length;
+class OffsetSourceFileLocation extends SourceFileLocation {
+  final int offset;
+  final String sourceName;
+  OffsetSourceFileLocation(SourceFile sourceFile, this.offset,
+      [this.sourceName]) : super(sourceFile);
+
+  String getSourceName() => sourceName;
 }