[dx] Turn on zero cost async stack traces by default.

Bug: v8:7522, v8:8673
Change-Id: Iee2d6fda9291fbdd346d25d2c535874dba13fdc9
Ref: nodejs/node#11865
Design-Document: http://bit.ly/v8-zero-cost-async-stack-traces
Reviewed-on: https://chromium-review.googlesource.com/c/1396425
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58765}

src/flag-definitions.h

@@ -1037,7 +1037,7 @@ DEFINE_BOOL(trace_sim_messages, false,
             "Trace simulator debug messages. Implied by --trace-sim.")
 
 // isolate.cc
-DEFINE_BOOL(async_stack_traces, false,
+DEFINE_BOOL(async_stack_traces, true,
             "include async stack traces in Error.stack")
 DEFINE_IMPLICATION(async_stack_traces, harmony_await_optimization)
 DEFINE_BOOL(stack_trace_on_illegal, false,

test/mjsunit/es8/async-function-stacktrace.js

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// Flags: --noasync-stack-traces
+
 async function test(func, funcs) {
   try {
     await func();