Fix type mismatch

This is tripping in DDC.  Trace and LazyTrace did not match.

R=nweiz@google.com

Review URL: https://codereview.chromium.org/992703002/

pkgs/stack_trace/lib/src/lazy_trace.dart

diff --git a/pkgs/stack_trace/lib/src/lazy_trace.dart b/pkgs/stack_trace/lib/src/lazy_trace.dart
index 21bb67f..6bfe51c 100644
--- a/pkgs/stack_trace/lib/src/lazy_trace.dart
+++ b/pkgs/stack_trace/lib/src/lazy_trace.dart
@@ -27,7 +27,7 @@
   List<Frame> get frames => _trace.frames;
   StackTrace get vmTrace => _trace.vmTrace;
   Trace get terse => new LazyTrace(() => _trace.terse);
-  Trace foldFrames(bool predicate(frame), {bool terse: false}) =>
+  Trace foldFrames(bool predicate(Frame frame), {bool terse: false}) =>
     new LazyTrace(() => _trace.foldFrames(predicate, terse: terse));
   String toString() => _trace.toString();