Make standalone tests not dependent on current working directory.

tests/standalone/full_coverage_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.
 
 // These tests fork a second VM process that runs the script
 // ``tools/full-coverage.dart'' and verifies that the tool
 // produces the expeced output.
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
 import 'package:path/path.dart' as path;
 import 'package:unittest/unittest.dart';
 
-final String coverageScript = "tools/full-coverage.dart";
+final String coverageScript =
+    Platform.script.resolve('../../tools/full-coverage.dart').toFilePath();
 final String packageRoot = Platform.packageRoot;
 final List dartBaseArgs = ['--package-root=${packageRoot}', '--checked',];
 
 // With line numbers starting at 0, the list of hits can be understood as
 // follows:
 // * -1: No coverage data on this line.
 // *  0: No hits on this line.
 // *  1: ``Some'' hits on this line.
 final coverageTests = [
   {
@@ skipping 195 matching lines @@
       String programPath = path.join(programDir, "${cTest['name']}.dart");
       testCoverage(programDir, programPath,
                    new LcovDescriptor(programPath),
                    new List.from(cTest['expectedHits']));
       testCoverage(programDir, programPath,
                    new PrettyPrintDescriptor(programPath),
                    new List.from(cTest['expectedHits']));
     });
   });
 }