Don't zone-register async callbacks for every await call in the VM.

runtime/vm/symbols.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_SYMBOLS_H_
 #define VM_SYMBOLS_H_
 
 #include "vm/object.h"
 #include "vm/snapshot_ids.h"
 
@@ skipping 85 matching lines @@
   V(On, "on")                                                                  \
   V(Of, "of")                                                                  \
   V(Deferred, "deferred")                                                      \
   V(Show, "show")                                                              \
   V(Hide, "hide")                                                              \
   V(Async, "async")                                                            \
   V(Sync, "sync")                                                              \
   V(YieldKw, "yield")                                                          \
   V(AsyncCompleter, ":async_completer")                                        \
   V(AsyncOperation, ":async_op")                                               \
+  V(AsyncThenCallback, ":async_op_then")                                       \
+  V(AsyncCatchErrorCallback, ":async_op_catch_error")                          \
   V(AsyncOperationParam, ":async_result")                                      \
   V(AsyncOperationErrorParam, ":async_error_param")                            \
   V(AsyncOperationStackTraceParam, ":async_stack_trace_param")                 \
   V(AsyncSavedTryCtxVarPrefix, ":async_saved_try_ctx_var_")                    \
   V(AsyncCatchHelper, "_asyncCatchHelper")                                     \
+  V(AsyncThenWrapperHelper, "_asyncThenWrapperHelper")                         \
+  V(AsyncErrorWrapperHelper, "_asyncErrorWrapperHelper")                       \
+  V(AsyncAwaitHelper, "_awaitHelper")                                          \
   V(Await, "await")                                                            \
   V(AwaitContextVar, ":await_ctx_var")                                         \
   V(AwaitJumpVar, ":await_jump_var")                                           \
   V(Future, "Future")                                                          \
   V(FutureMicrotask, "Future.microtask")                                       \
   V(FutureValue, "Future.value")                                               \
   V(FutureThen, "then")                                                        \
   V(FutureCatchError, "catchError")                                            \
   V(Completer, "Completer")                                                    \
   V(CompleterComplete, "complete")                                             \
@@ skipping 512 matching lines @@
   friend class SnapshotReader;
   friend class SnapshotWriter;
   friend class ApiMessageReader;
 
   DISALLOW_COPY_AND_ASSIGN(Symbols);
 };
 
 }  // namespace dart
 
 #endif  // VM_SYMBOLS_H_