Add diagnostic printing to standalone/precompilation_test.

tests/standalone/precompilation_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;
   }
 
+  print("Creating precompiled snapshot...");
   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}_bootstrap",
        ["--gen-precompiled-snapshot", Platform.script.path],
        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.
+    print("Creating shared library...");
     try {
       result = Process.runSync(
           cc,
           ["--version"],
           workingDirectory: tmp.path);
       if (result.exitCode != 0) {
         throw "$cc --version failed.";
       }
     } catch(e) {
       print("Skipping test because $cc is not present: $e");
       return;
     }
 
     result = Process.runSync(
         cc,
         [shared, cc_flags, "-nostartfiles", "-o", libname, "precompiled.S"],
         workingDirectory: tmp.path);
     if (result.exitCode != 0) {
       print(result.stdout);
       print(result.stderr);
       throw "Shared library creation failed!";
     }
 
+    print("Running test program...");
     var ld_library_path = new String.fromEnvironment("LD_LIBRARY_PATH");
     ld_library_path = "${ld_library_path}:${tmp.path}";
 
     result = Process.runSync(
        "${dart_executable}_precompiled_runtime",
        ["--run-precompiled-snapshot", "ignored_script", "--hello"],
        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") {
       throw "Precompiled binary output mismatch.";
     }
   } finally {
     tmp?.deleteSync(recursive: true);
   }
 }