Remove factory body in *.fromEnvironment, and implement this same behavior

pkg/compiler/lib/src/diagnostics/messages.dart

Index: pkg/compiler/lib/src/diagnostics/messages.dart
diff --git a/pkg/compiler/lib/src/diagnostics/messages.dart b/pkg/compiler/lib/src/diagnostics/messages.dart
index 6424772cfe7aabfff580b8a65835ba917077deb6..53b32a849323eefad77b43ae80b64b40a4c79b38 100644
--- a/pkg/compiler/lib/src/diagnostics/messages.dart
+++ b/pkg/compiler/lib/src/diagnostics/messages.dart
@@ -155,6 +155,7 @@ enum MessageKind {
   FORIN_NOT_ASSIGNABLE,
   FORMAL_DECLARED_CONST,
   FORMAL_DECLARED_STATIC,
+  FROM_ENVIRONMENT_MUST_BE_CONST,
   FUNCTION_TYPE_FORMAL_WITH_DEFAULT,
   FUNCTION_WITH_INITIALIZER,
   GENERIC,
@@ -1078,6 +1079,15 @@ main() => new C(0);"""
               "This const constructor is not allowed due to "
               "non-final fields."),
 
+      MessageKind.FROM_ENVIRONMENT_MUST_BE_CONST: const MessageTemplate(
+          MessageKind.FROM_ENVIRONMENT_MUST_BE_CONST,
+          "#{className}.fromEnvironment can only be used as a "
+          "const constructor.",
+          howToFix: "Try replacing `new` with `const`.",
+          examples: const [
+            "abstract class A {} main() { new bool.fromEnvironment('X'); }"

[Bob Nystrom, 2017/05/24 19:52:09]

What's the "abstract class A {}" part for?

[Siggi Cherem (dart-lang), 2017/05/24 20:37:19]

Thanks for catching that, I copied code form a different example, modified main
and missed the extra class definition. There is no need for it.

+          ]),
+
       MessageKind.INITIALIZING_FORMAL_NOT_ALLOWED: const MessageTemplate(
           MessageKind.INITIALIZING_FORMAL_NOT_ALLOWED,
           "Initializing formal parameter only allowed in generative "