Disable awaiter stepping by default until context level computation is fixed

runtime/vm/flag_list.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 RUNTIME_VM_FLAG_LIST_H_
 #define RUNTIME_VM_FLAG_LIST_H_
 
 // Don't use USING_DBC outside of this file.
 #if defined(TARGET_ARCH_DBC)
 #define USING_DBC true
@@ skipping 131 matching lines @@
     "Print live ranges after allocation.")                                     \
   C(print_stop_message, false, false, bool, false, "Print stop message.")      \
   D(print_variable_descriptors, bool, false,                                   \
     "Print variable descriptors in disassembly.")                              \
   R(profiler, false, bool, !USING_DBC && !USING_FUCHSIA,                       \
     "Enable the profiler.")                                                    \
   P(reorder_basic_blocks, bool, true, "Reorder basic blocks")                  \
   C(causal_async_stacks, false, false, bool, true, "Improved async stacks")    \
   C(stress_async_stacks, false, false, bool, false,                            \
     "Stress test async stack traces")                                          \
-  C(async_debugger_stepping, false, false, bool, true,                         \
+  C(async_debugger_stepping, false, false, bool, false,                        \
     "Debugger support for stepping in and out of async functions.")            \
   R(support_ast_printer, false, bool, true, "Support the AST printer.")        \
   R(support_compiler_stats, false, bool, true, "Support compiler stats.")      \
   C(support_debugger, false, false, bool, true, "Support the debugger.")       \
   R(support_disassembler, false, bool, true, "Support the disassembler.")      \
   R(support_il_printer, false, bool, true, "Support the IL printer.")          \
   C(support_reload, false, false, bool, true, "Support isolate reload.")       \
   R(support_service, false, bool, true, "Support the service protocol.")       \
   R(support_timeline, false, bool, true, "Support timeline.")                  \
   D(trace_cha, bool, false, "Trace CHA operations")                            \
@@ skipping 17 matching lines @@
   P(verbose_gc_hdr, int, 40, "Print verbose GC header interval.")              \
   R(verify_after_gc, false, bool, false,                                       \
     "Enables heap verification after GC.")                                     \
   R(verify_before_gc, false, bool, false,                                      \
     "Enables heap verification before GC.")                                    \
   D(verify_gc_contains, bool, false,                                           \
     "Enables verification of address contains during GC.")                     \
   D(verify_on_transition, bool, false, "Verify on dart <==> VM.")
 
 #endif  // RUNTIME_VM_FLAG_LIST_H_