Refactor SourceFile, SourceFileProvider and SourceLocation.

tests/compiler/dart2js/backend_dart/dart_printer_test.dart

 // Copyright (c) 2014, 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 dart_printer_test;
 
 import "package:expect/expect.dart";
 import 'package:compiler/src/constants/values.dart';
 import 'package:compiler/src/dart_backend/backend_ast_nodes.dart';
 import 'package:compiler/src/scanner/scannerlib.dart';
@@ skipping 640 matching lines @@
     }
   }
   else {
     if (x != y) {
       throw new Error();
     }
   }
 }
 
 Expression parseExpression(String code) {
-  SourceFile file = new StringSourceFile('', code);
+  SourceFile file = new StringSourceFile.fromName('', code);
   Scanner scan = new Scanner(file);
   Token tok = scan.tokenize();
   AstBuilder builder = new AstBuilder();
   Parser parser = new Parser(builder);
   tok = parser.parseExpression(tok);
   if (builder.stack.length != 1 || tok.kind != EOF_TOKEN) {
     throw "Parse error in $code";
   }
   return builder.pop();
 }
 Statement parseStatement(String code) {
-  SourceFile file = new StringSourceFile('', code);
+  SourceFile file = new StringSourceFile.fromName('', code);
   Scanner scan = new Scanner(file);
   Token tok = scan.tokenize();
   AstBuilder builder = new AstBuilder();
   Parser parser = new Parser(builder);
   tok = parser.parseStatement(tok);
   if (builder.stack.length != 1 || tok.kind != EOF_TOKEN) {
     throw "Parse error in $code";
   }
   return builder.pop();
 }
@@ skipping 39 matching lines @@
 void checkExpression(String code, [String expected="", String expected2=""]) {
   checkFn(code, expected, parseExpression, unparseExpression);
   checkFn(code, expected2, parseExpression, frontUnparseExpression);
 }
 void checkStatement(String code, [String expected="", String expected2=""]) {
   checkFn(code, expected, parseStatement, unparseStatement);
   checkFn(code, expected2, parseStatement, frontUnparseStatement);
 }
 
 void debugTokens(String code) {
-  SourceFile file = new StringSourceFile('', code);
+  SourceFile file = new StringSourceFile.fromName('', code);
   Scanner scan = new Scanner(file);
   Token tok = scan.tokenize();
   while (tok.next != tok) {
     print(tok.toString());
     tok = tok.next;
   }
 }
 
 void main() {
   // To check if these tests are effective, one should manually alter
@@ skipping 224 matching lines @@
   checkStatement("do while(x); while (y);");
   checkStatement("{do; while(x); while (y);}");
 
   checkStatement('switch(x) { case 1: case 2: return y; }');
   checkStatement('switch(x) { default: return y; }');
   checkStatement('switch(x) { case 1: x=y; default: return y; }');
   checkStatement('switch(x) { case 1: x=y; y=z; break; default: return y; }');
 
 }