Make lines and columns one-based in SourceLocation.

tests/compiler/dart2js/sourcemaps/sourcemap_helper.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 sourcemap.helper;
 
 import 'dart:async';
 import 'dart:io';
 import 'package:compiler/compiler_new.dart';
 import 'package:compiler/src/apiimpl.dart' as api;
@@ skipping 485 matching lines @@
   }
 
   void register(StepKind kind, js.Node node, {bool expectInfo: true}) {
     String dartCodeFromSourceLocation(SourceLocation sourceLocation) {
       SourceFile sourceFile =
           sourceFileManager.getSourceFile(sourceLocation.sourceUri);
       if (sourceFile == null) {
         return sourceLocation.shortText;
       }
       return sourceFile.kernelSource
-          .getTextLine(sourceLocation.line + 1)
-          .substring(sourceLocation.column)
+          .getTextLine(sourceLocation.line)
+          .substring(sourceLocation.column - 1)
           .trim();
     }
 
     void addLocation(SourceLocation sourceLocation, String jsCode) {
       if (sourceLocation == null) {
         if (expectInfo) {
           SourceInformation sourceInformation = node.sourceInformation;
           SourceLocation sourceLocation;
           String dartCode;
           if (sourceInformation != null) {
@@ skipping 53 matching lines @@
       absoluteUri = base.resolveUri(uri);
     } else {
       absoluteUri = base.resolve(uri);
     }
     return sourceFiles.putIfAbsent(absoluteUri, () {
       String text = new File.fromUri(absoluteUri).readAsStringSync();
       return new StringSourceFile.fromUri(absoluteUri, text);
     });
   }
 }