Ensure that constructor invocation file offset is set correctly for annotations.

Previously, the file offset pointed to the "@" token.  Now it points
to the constructor name, which makes more sense, and will simplify
integration with the analyzer.

Change-Id: I949d092abebf6a9e99f1d59285ca0ebcbc3b86cc
Reviewed-on: https://dart-review.googlesource.com/60808
Reviewed-by: Kevin Millikin <kmillikin@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index a3c3995..e4617ab 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -446,7 +446,7 @@
     if (arguments != null) {
       push(arguments);
       buildConstructorReferenceInvocation(
-          beginToken, beginToken.offset, Constness.explicitConst);
+          beginToken.next, beginToken.offset, Constness.explicitConst);
       push(popForValue());
     } else {
       String name = pop();