Throw an error early when dump info is used with the startup emitter.

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 48a3b537d7aef10773d20b7b96ff982dd504b168..3b9632c26b969e8b4e982b1c54db9a81c23887aa 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -334,6 +334,11 @@ abstract class Compiler implements LibraryLoaderListener {
       }
     }
 
+    if (options.dumpInfo && options.useStartupEmitter) {
+      throw new ArgumentError(
+          '--dump-info is not supported with the fast startup emitter');

[Harry Terkelsen, 2016/04/07 17:39:00]

I considered instead of crashing, just giving a warning and disabling dump-info
in this case, but I saw above that the compiler will crash if --dump-info is
enabled with dart2dart.

I'm open to either approach, let me know what you think

[Siggi Cherem (dart-lang), 2016/04/07 18:24:36]

fine with either too. This is probably easier to notice, so let's keep it.

+    }
+
     tasks = [
       dietParser = new DietParserTask(this, parsing.parserOptions),
       scanner = createScannerTask(),