- Refactor the way X.fromEnvironment is implemented.

tests/corelib/bool_from_environment_test.dart

Index: tests/corelib/bool_from_environment_test.dart
===================================================================
--- tests/corelib/bool_from_environment_test.dart	(revision 39888)
+++ tests/corelib/bool_from_environment_test.dart	(working copy)
@@ -11,4 +11,5 @@
   Expect.isTrue(const bool.fromEnvironment('c', defaultValue: true));
   Expect.isFalse(const bool.fromEnvironment('c', defaultValue: false));
   Expect.isFalse(const bool.fromEnvironment('d', defaultValue: false));
+  Expect.equals(const bool.fromEnvironment('dart.isVM'), !identical(1.0, 1));
 }