Reduce strong mode errors and warnings

pkg/front_end/lib/src/fasta/parser/parser.dart

Index: pkg/front_end/lib/src/fasta/parser/parser.dart
diff --git a/pkg/front_end/lib/src/fasta/parser/parser.dart b/pkg/front_end/lib/src/fasta/parser/parser.dart
index 8df334b42d206a606e830c13fb04299339a6eab6..7f78bf2906333385a6753db9d0d0897e700d4820 100644
--- a/pkg/front_end/lib/src/fasta/parser/parser.dart
+++ b/pkg/front_end/lib/src/fasta/parser/parser.dart
@@ -2453,7 +2453,7 @@ class Parser {
   Token parseParenthesizedExpression(Token token) {
     // We expect [begin] to be of type [BeginGroupToken], but we don't know for
     // sure until after calling expect.
-    var begin = token;
+    dynamic begin = token;
     token = expect('(', token);
     // [begin] is now known to have type [BeginGroupToken].
     token = parseExpression(token);