Add method on Value::IsAsyncFunction to detect async functions

DevTools wants to be able to detect async functions in order to print
their synopsis better in stack traces and tooltips. This patch provides a
simple method to do the check.

BUG=v8:4483

Review-Url: https://codereview.chromium.org/2365833002
Cr-Commit-Position: refs/heads/master@{#39687}

include/v8.h

@@ -2013,6 +2013,11 @@ class V8_EXPORT Value : public Data {
    */
   bool IsRegExp() const;
 
+  /**
+   * Returns true if this value is an async function.
+   */
+  bool IsAsyncFunction() const;
+
   /**
    * Returns true if this value is a Generator function.
    * This is an experimental feature.

src/api.cc

@@ -3384,6 +3384,12 @@ bool Value::IsRegExp() const {
   return obj->IsJSRegExp();
 }
 
+bool Value::IsAsyncFunction() const {
+  i::Handle<i::Object> obj = Utils::OpenHandle(this);
+  if (!obj->IsJSFunction()) return false;
+  i::Handle<i::JSFunction> func = i::Handle<i::JSFunction>::cast(obj);
+  return func->shared()->is_async();
+}
 
 bool Value::IsGeneratorFunction() const {
   i::Handle<i::Object> obj = Utils::OpenHandle(this);

test/cctest/test-api.cc

@@ -1581,6 +1581,26 @@ THREADED_TEST(IsGeneratorFunctionOrObject) {
   CHECK(!func->IsGeneratorObject());
 }
 
+THREADED_TEST(IsAsyncFunction) {
+  i::FLAG_harmony_async_await = true;
+  LocalContext env;
+  v8::Isolate* isolate = env->GetIsolate();
+  v8::HandleScope scope(isolate);
+
+  CompileRun("async function foo() {}");
+  v8::Local<Value> foo = CompileRun("foo");
+
+  CHECK(foo->IsAsyncFunction());
+  CHECK(foo->IsFunction());
+  CHECK(!foo->IsGeneratorFunction());
+  CHECK(!foo->IsGeneratorObject());
+
+  CompileRun("function bar() {}");
+  v8::Local<Value> bar = CompileRun("bar");
+
+  CHECK(!bar->IsAsyncFunction());
+  CHECK(bar->IsFunction());
+}
 
 THREADED_TEST(ArgumentsObject) {
   LocalContext env;