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 8de8da74f5a97ae6d7b161b50caf6bc8f27f2b05..8f917ec4c1b777af9d77ed033b534de2bcebb4b6 100644
--- a/pkg/front_end/lib/src/fasta/parser/parser.dart
+++ b/pkg/front_end/lib/src/fasta/parser/parser.dart
@@ -2451,8 +2451,9 @@ 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;
+    var first = token;
     token = expect('(', token);
+    BeginGroupToken begin = first;

[ahe, 2017/02/07 11:03:08]

I would rather keep the previous version using "dynamic". In this case, I feel
the documentation is adequate for explaining what is going on.

[Siggi Cherem (dart-lang), 2017/02/07 21:59:26]

Done.

     // [begin] is now known to have type [BeginGroupToken].
     token = parseExpression(token);
     if (!identical(begin.endGroup, token)) {