Add support for 'dart.library.X' environment variables in dart2js.

tests/language/library_env_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.
+
+import 'package:expect/expect.dart';
+
+main() {
+  const NOT_PRESENT = null;
+
+  Expect.isTrue(const bool.fromEnvironment("dart.library.async"));
+  Expect.isTrue(const bool.fromEnvironment("dart.library.collection"));
+  Expect.isTrue(const bool.fromEnvironment("dart.library.convert"));
+  Expect.isTrue(const bool.fromEnvironment("dart.library.core"));
+  Expect.isTrue(const bool.fromEnvironment("dart.library.typed_data"));
+
+
+  bool hasHtmlSupport;
+  hasHtmlSupport = true;   /// has_html_support: ok
+  hasHtmlSupport = false;  /// has_no_html_support: ok
+
+  if (hasHtmlSupport != null) {
+    bool expectedResult = hasHtmlSupport ? true : NOT_PRESENT;
+
+    Expect.equals(expectedResult,
+        const bool.fromEnvironment("dart.library.html",
+            defaultValue: NOT_PRESENT));
+    Expect.equals(expectedResult,
+        const bool.fromEnvironment("dart.library.indexed_db",
+            defaultValue: NOT_PRESENT));
+    Expect.equals(expectedResult,
+        const bool.fromEnvironment("dart.library.svg",
+            defaultValue: NOT_PRESENT));
+    Expect.equals(expectedResult,
+        const bool.fromEnvironment("dart.library.web_audio",
+            defaultValue: NOT_PRESENT));
+    Expect.equals(expectedResult,
+        const bool.fromEnvironment("dart.library.web_gl",
+            defaultValue: NOT_PRESENT));
+    Expect.equals(expectedResult,
+        const bool.fromEnvironment("dart.library.web_sql",
+            defaultValue: NOT_PRESENT));
+  }
+
+  bool hasIoSupport;
+  hasIoSupport = true;   /// has_io_support: ok
+  hasIoSupport = false;  /// has_no_io_support: ok
+
+  if (hasIoSupport != null) {
+    bool expectedResult = hasIoSupport ? true : NOT_PRESENT;
+
+    Expect.equals(expectedResult,
+        const bool.fromEnvironment("dart.library.io",
+            defaultValue: NOT_PRESENT));
+    Expect.equals(expectedResult,
+        const bool.fromEnvironment("dart.library.developer",
+            defaultValue: NOT_PRESENT));
+  }
+
+  bool hasMirrorSupport;
+  hasMirrorSupport = true;   /// has_mirror_support: ok
+  hasMirrorSupport = false;  /// has_no_mirror_support: ok
+
+  if (hasMirrorSupport != null) {
+    bool expectedResult = hasMirrorSupport ? true : NOT_PRESENT;
+
+    Expect.equals(expectedResult,
+        const bool.fromEnvironment("dart.library.mirrors",
+            defaultValue: NOT_PRESENT));
+  }
+
+  Expect.equals(NOT_PRESENT,
+      const bool.fromEnvironment("dart.library.XYZ",
+          defaultValue: NOT_PRESENT));
+  Expect.equals(NOT_PRESENT,
+      const bool.fromEnvironment("dart.library.Collection",
+          defaultValue: NOT_PRESENT));
+  Expect.equals(NOT_PRESENT,
+      const bool.fromEnvironment("dart.library.converT",
+          defaultValue: NOT_PRESENT));
+  Expect.equals(NOT_PRESENT,
+      const bool.fromEnvironment("dart.library.",
+          defaultValue: NOT_PRESENT));
+  Expect.equals(NOT_PRESENT,
+      const bool.fromEnvironment("dart.library.core ",
+          defaultValue: NOT_PRESENT));
+
+}