Rename RuntimeError to CyclicIntializationError, as per spec.

runtime/bin/vmstats/bargraph.dart

Index: runtime/bin/vmstats/bargraph.dart
diff --git a/runtime/bin/vmstats/bargraph.dart b/runtime/bin/vmstats/bargraph.dart
index 89b00a49d428c0eca5eef49724bf782857dd8d6a..b9deb1e6dea2fe4187418d7aa4f97ccb084dd1d1 100644
--- a/runtime/bin/vmstats/bargraph.dart
+++ b/runtime/bin/vmstats/bargraph.dart
@@ -31,7 +31,7 @@ class BarGraph {
 
   void addSample(List<int> segments) {
     if (segments.length != _elements.length) {
-      throw new RuntimeError('invalid sample size for graph');
+      throw new ArgumentError('invalid sample size for graph');
     }
     _model.addSample(segments);
   }