update fasta scanner to always generate INDEX or INDEX_EQ tokens

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 ecbe4830c05cf231681d0b393da6e1064ca9ef96..410e465229f9364274143149a225d4daab98a441 100644
--- a/pkg/front_end/lib/src/fasta/parser/parser.dart
+++ b/pkg/front_end/lib/src/fasta/parser/parser.dart
@@ -492,6 +492,10 @@ class Parser {
         token = parseOptionalFormalParameters(token, true,
             inFunctionType: inFunctionType);
         break;
+      } else if (identical(value, '[]')) {
+        reportRecoverableError(token,

[ahe, 2017/03/09 12:45:18]

Nice. This should work well with endFormalParameters being called with
parameterCount == 0 below.

The new error may change the status of some tests. Be sure to test -cdartk:

./tools/build.py -mrelease runtime_kernel && ./tools/test.py -mrelease -cdartk
co19 language kernel --time -pcolor --report --failure-summary -j16

You may need to update these files:

tests/co19/co19-kernel.status
tests/kernel/kernel.status
tests/language/language_kernel.status

+            ErrorKind.EmptyOptionalParameterList);
+        break;
       }
       token = parseFormalParameter(token, FormalParameterType.REQUIRED,
           inFunctionType: inFunctionType);