Improve precision of JS printer callbacks (2nd try)

pkg/compiler/lib/src/io/source_information.dart

 // Copyright (c) 2015, 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 dart2js.source_information;
 
 import '../dart2jslib.dart' show SourceSpan;
 import '../elements/elements.dart' show AstElement;
 import '../scanner/scannerlib.dart' show Token;
 import '../tree/tree.dart' show Node;
 import '../js/js.dart' show JavaScriptNodeSourceInformation;
-import 'code_output.dart';
 import 'source_file.dart';
 
 /// Interface for passing source information, for instance for use in source
 /// maps, through the backend.
 abstract class SourceInformation extends JavaScriptNodeSourceInformation {
   SourceSpan get sourceSpan;
-  void beginMapping(CodeOutput output);
-  void endMapping(CodeOutput output);
+
+  /// The source location associated with the start of the JS node.
+  SourceLocation get startPosition;
+
+  /// The source location associated with the end of the JS node.
+  SourceLocation get endPosition;
 }
 
 /// Source information that contains start source position and optionally an
 /// end source position.
 class StartEndSourceInformation implements SourceInformation {
   final SourceLocation startPosition;
   final SourceLocation endPosition;
 
   StartEndSourceInformation(this.startPosition, [this.endPosition]);
 
   SourceSpan get sourceSpan {
     Uri uri = startPosition.sourceUri;
     int begin = startPosition.offset;
     int end = endPosition == null ? begin : endPosition.offset;
     return new SourceSpan(uri, begin, end);
   }
 
-  void beginMapping(CodeBuffer output) {
-    output.beginMappedRange();
-    output.setSourceLocation(startPosition);
-  }
-
-  void endMapping(CodeBuffer output) {
-    if (endPosition != null) {
-      output.setSourceLocation(endPosition);
-    }
-    output.endMappedRange();
-  }
-
   int get hashCode {
     return (startPosition.hashCode * 17 +
             endPosition.hashCode * 19)
            & 0x7FFFFFFF;
   }
 
   bool operator ==(other) {
     if (identical(this, other)) return true;
     if (other is! StartEndSourceInformation) return false;
     return startPosition == other.startPosition &&
@@ skipping 44 matching lines @@
   }
 }
 
 /// [SourceInformation] that consists of an offset position into the source
 /// code.
 class PositionSourceInformation implements SourceInformation {
   final SourceLocation sourcePosition;
 
   PositionSourceInformation(this.sourcePosition);
 
-  @override
-  void beginMapping(CodeOutput output) {
-    output.setSourceLocation(sourcePosition);
-  }
-
-  @override
-  void endMapping(CodeOutput output) {
-    // Do nothing.
-  }
+  SourceLocation get startPosition => sourcePosition;
+  SourceLocation get endPosition => null;
 
   SourceSpan get sourceSpan {
     Uri uri = sourcePosition.sourceUri;
     int offset = sourcePosition.offset;
     return new SourceSpan(uri, offset, offset);
   }
 
   int get hashCode {
     return sourcePosition.hashCode * 17 & 0x7FFFFFFF;
   }
@@ skipping 70 matching lines @@
   TokenSourceLocation(SourceFile sourceFile, this.token, this.sourceName)
     : super(sourceFile);
 
   @override
   int get offset => token.charOffset;
 
   String toString() {
     return '${super.toString()}:$sourceName';
   }
 }