Add test precompiling dart2js.

tests/standalone/precompilation_dart2js_test.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.
 
 // Test generating and running a simple precompiled snapshot of this script.
 
 import 'dart:io';
 
 main(List args) {
   if (args.length > 0 && args[0] == "--hello") {
@@ skipping 25 matching lines @@
     cc_flags = "-m32";
   } else if (Platform.version.contains("arm")) {
     cc_flags = "";
   } else if (Platform.version.contains("mips")) {
     cc_flags = "-EL";
   } else {
     print("Architecture not supported: ${Platform.version}");
     return;
   }
 
+  var abs_package_root = new File(Platform.packageRoot).absolute.path;
   var dart_executable =
       Directory.current.path + Platform.pathSeparator + Platform.executable;
   Directory tmp;
   try {
     tmp = Directory.current.createTempSync("temp_precompilation_test");
-    var result = Process.runSync(
-       "${dart_executable}_no_snapshot",
-       ["--gen-precompiled-snapshot", Platform.script.path],
-       workingDirectory: tmp.path);
+    var exec = "${dart_executable}_no_snapshot";
+    var args = ["--package-root=$abs_package_root",
+                "--gen-precompiled-snapshot",
+                "${abs_package_root}compiler/src/dart2js.dart"];
+    print("$exec ${args.join(' ')}");
+    var result = Process.runSync(exec, args, workingDirectory: tmp.path);
     if (result.exitCode != 0) {
       print(result.stdout);
       print(result.stderr);
       throw "Snapshot generation failed.";
     }
 
     // Check if gcc is present, and skip test if it is not.
     try {
       result = Process.runSync(
           cc,
@@ skipping 12 matching lines @@
         [shared, cc_flags, "-o", libname, "precompiled.S"],
         workingDirectory: tmp.path);
     if (result.exitCode != 0) {
       print(result.stdout);
       print(result.stderr);
       throw "Shared library creation failed!";
     }
 
     var ld_library_path = new String.fromEnvironment("LD_LIBRARY_PATH");
     ld_library_path = "${ld_library_path}:${tmp.path}";
-
-    result = Process.runSync(
-       "${dart_executable}",
-       ["--run-precompiled-snapshot", "ignored_script", "--hello"],
+    exec = "${dart_executable}";
+    args = ["--run-precompiled-snapshot", "ignored_script", "--version"];
+    print("LD_LIBRARY_PATH=$ld_library_path $exec ${args.join(' ')}");
+    result = Process.runSync(exec, args,
        workingDirectory: tmp.path,
        environment: {"LD_LIBRARY_PATH": ld_library_path});
     if (result.exitCode != 0) {
       print(result.stdout);
       print(result.stderr);
       throw "Precompiled binary failed.";
     }
     print(result.stdout);
-    if (result.stdout != "Hello\n") {
+    if (!result.stdout.contains("Dart-to-JavaScript compiler")) {
       throw "Precompiled binary output mismatch.";
     }
   } finally {
     tmp?.deleteSync(recursive: true);
   }
 }