Implement type inference for try/catch blocks.

pkg/front_end/testcases/expressions.dart.direct.expect

Index: pkg/front_end/testcases/expressions.dart.direct.expect
diff --git a/pkg/front_end/testcases/expressions.dart.direct.expect b/pkg/front_end/testcases/expressions.dart.direct.expect
index 0f7087de8274083fa2bf531f739779434d1bc6fc..11c1f31a5a35b8aff9240567b2323392d9b6e456 100644
--- a/pkg/front_end/testcases/expressions.dart.direct.expect
+++ b/pkg/front_end/testcases/expressions.dart.direct.expect
@@ -21,7 +21,7 @@ static method main() → dynamic {
   try {
     throw "fisk";
   }
-  on core::String catch(final dynamic e, final dynamic s) {
+  on core::String catch(final core::String e, final core::StackTrace s) {
     core::print(e);
     if(!s.==(null))
       core::print(s);
@@ -72,7 +72,7 @@ static method main() → dynamic {
     core::print(throw new core::NoSuchMethodError::_withType(null, #toString, 32, <dynamic>[].toList(growable: false), <dynamic, dynamic>{}, null));
     throw "Shouldn't work";
   }
-  on core::NoSuchMethodError catch(final dynamic e) {
+  on core::NoSuchMethodError catch(final core::NoSuchMethodError e) {
     core::print("As expected: ${e}");
   }
   core::print(core::int::parse("42"));