Rename RuntimeError to CyclicIntializationError, as per spec.

sdk/lib/_internal/compiler/implementation/lib/js_helper.dart

Index: sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
index ab36275286da195ec31e8e5a5ba009c5dc01cc14..554357e35bd526803a1ad0635ac49e1f3fc44cc5 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
@@ -1444,5 +1444,15 @@ void throwNoSuchMethod(obj, name, arguments, expectedArgumentNames) {
  * field that is currently being initialized.
  */
 void throwCyclicInit(String staticName) {
-  throw new RuntimeError("Cyclic initialization for static $staticName");
+  throw new CyclicInitializationError(
+      "Cyclic initialization for static $staticName");
+}
+
+/**
+ * Error thrown when a runtime error occurs.
+ */
+class RuntimeError implements Error {
+  final message;
+  RuntimeError(this.message);
+  String toString() => "RuntimeError: $message";
 }