dart2Js: bailout early when using the new emitter with mirrors.

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index 5427478abab9278d3dc11d409734ffd150fd40d9..12ad4a787e05fe3c14d9f837b63924d17398b9fb 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -1220,6 +1220,12 @@ abstract class Compiler implements DiagnosticListener {
     } else if (uri == DART_NATIVE_TYPED_DATA) {
       typedDataLibrary = library;
     } else if (uri == DART_MIRRORS) {
+      if (const bool.fromEnvironment("dart2js.use.new.emitter")) {
+        internalError(library,

[floitsch, 2015/02/27 14:05:50]

This should not be an internal error, but a "reportError" or similar. The string
should be in "warnings.dart".

I would put this close to the already existing warning in line 1325.

[zarah, 2015/03/02 10:42:36]

Done.

+            "dart:mirrors library is not supported when using the new emitter "
+            "(DART_VM_OPTIONS='-Ddart2js.use.new.emitter=true')");
+      }
+
       mirrorsLibrary = library;
     }
     backend.onLibraryCreated(library);