Fix all strong mode errors and warnings.

lib/src/tokenizer.dart

Index: lib/src/tokenizer.dart
diff --git a/lib/src/tokenizer.dart b/lib/src/tokenizer.dart
index d423104bae92eb05e5a278fb249e603021de8486..bc00fee480ed5dfaea4272c22780a5ccebefbc05 100644
--- a/lib/src/tokenizer.dart
+++ b/lib/src/tokenizer.dart
@@ -260,7 +260,7 @@ class Tokenizer extends TokenizerBase {
   Token finishIdentifier() {
     // If we encounter an escape sequence, remember it so we can post-process
     // to unescape.
-    var chars = [];
+    var chars = <int>[];
 
     // backup so we can start with the first character
     int validateFrom = _index;