Rename RuntimeError to CyclicIntializationError, as per spec.

runtime/vm/snapshot_test.cc

Index: runtime/vm/snapshot_test.cc
diff --git a/runtime/vm/snapshot_test.cc b/runtime/vm/snapshot_test.cc
index f80bb246bc0295a37cfb204335691c9ff45b3e32..d0d33653d5ffc4c27325246fb8147eb84c6235ed 100644
--- a/runtime/vm/snapshot_test.cc
+++ b/runtime/vm/snapshot_test.cc
@@ -920,7 +920,7 @@ UNIT_TEST_CASE(FullSnapshot) {
       "}\n"
       "class Expect {\n"
       "  static void equals(x, y) {\n"
-      "    if (x != y) throw new RuntimeError('not equal');\n"
+      "    if (x != y) throw new ArgumentError('not equal');\n"
       "  }\n"
       "}\n"
       "class FieldsTest {\n"