Improve error handling in the process library.

tests/standalone/src/ProcessInvalidArgumentsTest.dart

+// Copyright (c) 2011, 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.
+//
+// Process test program to test that invalid arguments throw exceptions.
+
+void testNonStringPath() {
+  try {
+    Process p = new Process(["true"], []);
+    Expect.fail("Did not throw exception");
+  } catch(var e) {
+    Expect.isTrue(e is ProcessException, "Wrong exception type: $e");
+  }
+}
+
+void testNonListArguments() {
+  try {
+    Process p = new Process("true", "asdf");
+    Expect.fail("Did not throw exception");
+  } catch(var e) {
+    Expect.isTrue(e is ProcessException, "Wrong exception type: $e");
+  }
+}
+
+void testNonStringArgument() {
+  try {
+    Process p = new Process("true", ["asdf", 1]);
+    Expect.fail("Did not throw exception");
+  } catch(var e) {
+    Expect.isTrue(e is ProcessException, "Wrong exception type: $e");
+  }
+}
+
+class MyString implements String {
+  MyString();
+}
+
+void testMyStringArgument() {
+  Process p = new Process("true", [new MyString()]);
+  try {
+    p.start();
+    Expect.fail("Did not throw exception");
+  } catch(var e) {
+    Expect.isTrue(e is ProcessException, "Wrong exception type: $e");
+  }
+}
+
+void testMyStringPath() {
+  Process p = new Process(new MyString(), ['asdf']);
+  try {
+    p.start();
+    Expect.fail("Did not throw exception");
+  } catch(var e) {
+    Expect.isTrue(e is ProcessException, "Wrong exception type: $e");
+  }
+}
+
+void main() {
+  testNonStringPath();
+  testNonListArguments();
+  testNonStringArgument();
+  testMyStringArgument();
+  testMyStringPath();
+}