Fix build breakage caused by the recent toString() commit.

frog/leg/lib/coreimpl.dart

Index: frog/leg/lib/coreimpl.dart
diff --git a/frog/leg/lib/coreimpl.dart b/frog/leg/lib/coreimpl.dart
index af593ac535c00582bc112cf64d5832a673005f8e..06b8767604b334d006474bafd7cb420e3b7c8337 100644
--- a/frog/leg/lib/coreimpl.dart
+++ b/frog/leg/lib/coreimpl.dart
@@ -6,6 +6,7 @@
 
 #import('js_helper.dart');
 
+#source('../../../corelib/src/implementation/collections.dart');
 #source('../../../corelib/src/implementation/dual_pivot_quicksort.dart');
 #source('../../../corelib/src/implementation/duration_implementation.dart');
 #source('../../../corelib/src/implementation/exceptions.dart');
@@ -19,6 +20,5 @@
 #source('../../../corelib/src/implementation/stopwatch_implementation.dart');
 
 #source('../../../runtime/lib/arrays.dart');
-#source('../../../runtime/lib/collections.dart');
 
 #source('mockimpl.dart');