Fix shift in source map positions.

pkg/compiler/lib/src/io/line_column_provider.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 dart2js.io.line_column;
 
 import 'code_output.dart';
 
 /// Interface for providing line/column information.
 abstract class LineColumnProvider {
   /// Returns the line number (0-based) for [offset].
   int getLine(int offset);
 
   /// Returns the column number (0-based) for [offset] at the given [line].
   int getColumn(int line, int offset);
 }
 
 /// [CodeOutputListener] that collects line information.
 class LineColumnCollector extends CodeOutputListener
     implements LineColumnProvider {
-  int lastLineStart = 0;
+  int length = 0;
   List<int> lineStarts = <int>[0];
 
   void _collect(String text) {
-    int offset = lastLineStart;
     int index = 0;
     while (index < text.length) {
       // Unix uses '\n' and Windows uses '\r\n', so this algorithm works for
       // both platforms.
       index = text.indexOf('\n', index) + 1;
       if (index <= 0) break;
-      lastLineStart = offset + index;
-      lineStarts.add(lastLineStart);
+      lineStarts.add(length + index);
     }
+    length += text.length;
   }
 
   @override
   void onText(String text) {
     _collect(text);
   }
 
   @override
   int getLine(int offset) {
     List<int> starts = lineStarts;
     if (offset < 0 || starts.last <= offset) {
-      throw 'bad position #$offset in buffer with length ${lineStarts.last}.';
+      throw 'bad position #$offset in buffer with length ${length}.';
     }
     int first = 0;
     int count = starts.length;
     while (count > 1) {
       int step = count ~/ 2;
       int middle = first + step;
       int lineStart = starts[middle];
       if (offset < lineStart) {
         count = step;
       } else {
         first = middle;
         count -= step;
       }
     }
     return first;
   }
 
   @override
   int getColumn(int line, int offset) {
     return offset - lineStarts[line];
   }
 
   @override
   void onDone(int length) {
-    lineStarts.add(length);
+    lineStarts.add(length + 1);
+    this.length = length;
+  }
+
+  String toString() {
+    return 'lineStarts=$lineStarts,length=$length';
   }
 }