Fix type warnings and a few other warnings, and probably even an error.

lib/compiler/implementation/scanner/parser_bench.dart

Index: lib/compiler/implementation/scanner/parser_bench.dart
diff --git a/lib/compiler/implementation/scanner/parser_bench.dart b/lib/compiler/implementation/scanner/parser_bench.dart
index a81632f9f0cc821aafae661530e3ee5cee4d1006..c8f6cc0bba521e64f0bf442f1318e0ce48b8de24 100644
--- a/lib/compiler/implementation/scanner/parser_bench.dart
+++ b/lib/compiler/implementation/scanner/parser_bench.dart
@@ -12,7 +12,7 @@ class ParserBench extends BaseParserBench {
   Token scanFileNamed(String filename) {
     Token token;
     getBytes(filename, (bytes) {
-      Scanner scanner = makeScanner(bytes);
+      AbstractScanner scanner = makeScanner(bytes);
       try {
         token = scanner.tokenize();
         printTokens(token);