Disable async debugger support until context mismatch issue is resolved.

BUG=
R=rmacnak@google.com

Review-Url: https://codereview.chromium.org/2795303002 .
diff --git a/runtime/observatory/tests/service/async_single_step_exception_test.dart b/runtime/observatory/tests/service/async_single_step_exception_test.dart
index 365aab7..4307872 100644
--- a/runtime/observatory/tests/service/async_single_step_exception_test.dart
+++ b/runtime/observatory/tests/service/async_single_step_exception_test.dart
@@ -1,7 +1,7 @@
 // Copyright (c) 2017, 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.
-// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug
+// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug --async_debugger
 
 import 'dart:async';
 import 'dart:developer';
diff --git a/runtime/observatory/tests/service/async_single_step_into_test.dart b/runtime/observatory/tests/service/async_single_step_into_test.dart
index 7b7f786..129ff6a 100644
--- a/runtime/observatory/tests/service/async_single_step_into_test.dart
+++ b/runtime/observatory/tests/service/async_single_step_into_test.dart
@@ -1,7 +1,7 @@
 // Copyright (c) 2017, 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.
-// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug
+// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug --async_debugger
 
 import 'dart:developer';
 import 'package:observatory/models.dart' as M;
diff --git a/runtime/observatory/tests/service/async_single_step_out_test.dart b/runtime/observatory/tests/service/async_single_step_out_test.dart
index 97e4942..f66360f 100644
--- a/runtime/observatory/tests/service/async_single_step_out_test.dart
+++ b/runtime/observatory/tests/service/async_single_step_out_test.dart
@@ -1,7 +1,7 @@
 // Copyright (c) 2017, 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.
-// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug
+// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug --async_debugger
 
 import 'dart:developer';
 import 'package:observatory/models.dart' as M;
diff --git a/runtime/observatory/tests/service/async_star_single_step_into_test.dart b/runtime/observatory/tests/service/async_star_single_step_into_test.dart
index 1575251..ddfa210 100644
--- a/runtime/observatory/tests/service/async_star_single_step_into_test.dart
+++ b/runtime/observatory/tests/service/async_star_single_step_into_test.dart
@@ -1,7 +1,7 @@
 // Copyright (c) 2017, 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.
-// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug
+// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug --async_debugger
 
 import 'dart:developer';
 import 'package:observatory/models.dart' as M;
diff --git a/runtime/observatory/tests/service/async_star_step_out_test.dart b/runtime/observatory/tests/service/async_star_step_out_test.dart
index c57862a..a59f955 100644
--- a/runtime/observatory/tests/service/async_star_step_out_test.dart
+++ b/runtime/observatory/tests/service/async_star_step_out_test.dart
@@ -1,7 +1,7 @@
 // Copyright (c) 2017, 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.
-// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug
+// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug --async_debugger
 
 import 'dart:developer';
 import 'package:observatory/models.dart' as M;
diff --git a/runtime/observatory/tests/service/async_step_out_test.dart b/runtime/observatory/tests/service/async_step_out_test.dart
index 0acff6a..8c6718c 100644
--- a/runtime/observatory/tests/service/async_step_out_test.dart
+++ b/runtime/observatory/tests/service/async_step_out_test.dart
@@ -1,7 +1,7 @@
 // Copyright (c) 2017, 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.
-// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug
+// VMOptions=--error_on_bad_type --error_on_bad_override  --verbose_debug --async_debugger
 
 import 'dart:developer';
 import 'package:observatory/models.dart' as M;
diff --git a/runtime/vm/debugger.cc b/runtime/vm/debugger.cc
index 63760c0..d53e39a 100644
--- a/runtime/vm/debugger.cc
+++ b/runtime/vm/debugger.cc
@@ -3242,7 +3242,7 @@
 
 
 void Debugger::RememberTopFrameAwaiter() {
-  if (!FLAG_async_debugger_stepping) {
+  if (!FLAG_async_debugger) {
     return;
   }
   if (stack_trace_->Length() > 0) {
@@ -3254,7 +3254,7 @@
 
 
 void Debugger::SetAsyncSteppingFramePointer() {
-  if (!FLAG_async_debugger_stepping) {
+  if (!FLAG_async_debugger) {
     return;
   }
   if (stack_trace_->FrameAt(0)->function().IsAsyncClosure() ||
@@ -3294,7 +3294,7 @@
       OS::Print("HandleSteppingRequest- kStepOver %" Px "\n", stepping_fp_);
     }
   } else if (resume_action_ == kStepOut) {
-    if (FLAG_async_debugger_stepping) {
+    if (FLAG_async_debugger) {
       if (stack_trace->FrameAt(0)->function().IsAsyncClosure() ||
           stack_trace->FrameAt(0)->function().IsAsyncGenClosure()) {
         // Request to step out of an async/async* closure.
@@ -3662,7 +3662,7 @@
   ActivationFrame* frame = TopDartFrame();
   ASSERT(frame != NULL);
 
-  if (FLAG_async_debugger_stepping) {
+  if (FLAG_async_debugger) {
     if ((async_stepping_fp_ != 0) && (top_frame_awaiter_ != Object::null())) {
       // Check if the user has single stepped out of an async function with
       // an awaiter. The first check handles the case of calling into the
@@ -4299,7 +4299,7 @@
 
 
 void Debugger::MaybeAsyncStepInto(const Closure& async_op) {
-  if (FLAG_async_debugger_stepping && IsSingleStepping()) {
+  if (FLAG_async_debugger && IsSingleStepping()) {
     // We are single stepping, set a breakpoint on the closure activation
     // and resume execution so we can hit the breakpoint.
     AsyncStepInto(async_op);
diff --git a/runtime/vm/flag_list.h b/runtime/vm/flag_list.h
index e8fcc0c..85f74c4 100644
--- a/runtime/vm/flag_list.h
+++ b/runtime/vm/flag_list.h
@@ -149,8 +149,8 @@
   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,                         \
-    "Debugger support for stepping in and out of async functions.")            \
+  C(async_debugger, false, false, bool, false,                                 \
+    "Debugger support 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.")       \
diff --git a/runtime/vm/object_store.cc b/runtime/vm/object_store.cc
index f1dcac5..5b2ffcc 100644
--- a/runtime/vm/object_store.cc
+++ b/runtime/vm/object_store.cc
@@ -273,7 +273,7 @@
                                       function_name, 2, Object::null_array());
   ASSERT(!function.IsNull());
   set_complete_on_async_return(function);
-  if (FLAG_async_debugger_stepping) {
+  if (FLAG_async_debugger) {
     // Disable debugging and inlining the _CompleteOnAsyncReturn function.
     function.set_is_debuggable(false);
     function.set_is_inlinable(false);
@@ -284,7 +284,7 @@
   ASSERT(!cls.IsNull());
   set_async_star_stream_controller(cls);
 
-  if (FLAG_async_debugger_stepping) {
+  if (FLAG_async_debugger) {
     // Disable debugging and inlining of all functions on the
     // _AsyncStarStreamController class.
     const Array& functions = Array::Handle(cls.functions());