[promises] Add %WaitForPromise runtime call to allow tests to reliably wait for promises to be fini…

src/runtime/runtime-promise.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/counters.h"
 #include "src/debug/debug.h"
 #include "src/elements.h"
 #include "src/objects-inl.h"
@@ skipping 144 matching lines @@
     isolate->RunPromiseHook(PromiseHookType::kBefore,
                             Handle<JSPromise>::cast(promise),
                             isolate->factory()->undefined_value());
   }
   return isolate->heap()->undefined_value();
 }
 
 RUNTIME_FUNCTION(Runtime_PromiseHookAfter) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
-  CONVERT_ARG_HANDLE_CHECKED(JSObject, promise, 0);
-  if (promise->IsJSPromise()) {
+  CONVERT_ARG_HANDLE_CHECKED(JSObject, arg, 0);
+  if (arg->IsJSPromise()) {
     isolate->RunPromiseHook(PromiseHookType::kAfter,
-                            Handle<JSPromise>::cast(promise),
+                            Handle<JSPromise>::cast(arg),
                             isolate->factory()->undefined_value());
   }
   return isolate->heap()->undefined_value();
 }
 
+RUNTIME_FUNCTION(Runtime_IncrementWaitCount) {

[gsathya, 2017/03/16 17:39:04]

Can you move these to runtime-test.cc? 

+  isolate->IncrementWaitCountForTesting();
+  return isolate->heap()->undefined_value();
+}
+
+RUNTIME_FUNCTION(Runtime_DecrementWaitCount) {
+  isolate->DecrementWaitCountForTesting();
+  return isolate->heap()->undefined_value();
+}
 }  // namespace internal
 }  // namespace v8