add _CompileTimeError error to dart2js patch

sdk/lib/_internal/js_runtime/lib/core_patch.dart

Index: sdk/lib/_internal/js_runtime/lib/core_patch.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/core_patch.dart b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
index 3dfa7f068e95143ece9566df9201230cdce72e5b..7c7be1d29024e82710d27fabbcfb86139e39d9ff 100644
--- a/sdk/lib/_internal/js_runtime/lib/core_patch.dart
+++ b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
@@ -606,6 +606,12 @@ class NoSuchMethodError {
   }
 }
 
+class _CompileTimeError extends Error {
+  final String _errorMsg;
+  _CompileTimeError(this._errorMsg);

[ahe, 2017/05/24 19:53:31]

Consider adding this body:

{ JS("", "debug"); }

[Siggi Cherem (dart-lang), 2017/05/24 20:14:18]

not sure I follow - did you mean 'debugger' to set a breakpoint preemptively?

If so - I'm not convinced, I think without it we give users more flexibility.
For exampale, with `debugger`, the only way to proceed is to skip each debugger
call by hand. Without it users can use stop-on-unhandled-exceptions if they want
to stop, or disable that if just want to see errors in the console. 

[ahe, 2017/05/24 20:19:11]

Yes, I meant "debugger". This is what the specification says:

If an uncaught compile-time error occurs within the code of a running isolate
$A$, $A$ is immediately suspended.

Rationale: you don't want to be able to catch a compile-time error as a regular
exception.

+  String toString() => _errorMsg;
+}
+
 @patch
 class Uri {
   @patch