Add missing custom-allocation routine for InlineTaskDetached

Summary:
Allocation of InlineTaskDetached coroutines now call through to the
folly_coro_async_malloc() and folly_coro_async_free() functions so that
their allocations can be correctly accounted for as coroutine allocations.

Reviewed By: yfeldblum

Differential Revision: D24574568

fbshipit-source-id: 9bece3f8e6f6d221bca021a50fe02e1eed88f07b

folly/experimental/coro/detail/InlineTask.h

@@ -242,6 +242,14 @@ inline InlineTask<void> InlineTaskPromise<void>::get_return_object() noexcept {
 struct InlineTaskDetached {
   class promise_type {
    public:
+    static void* operator new(std::size_t size) {
+      return ::folly_coro_async_malloc(size);
+    }
+
+    static void operator delete(void* ptr, std::size_t size) {
+      ::folly_coro_async_free(ptr, size);
+    }
+
     InlineTaskDetached get_return_object() noexcept { return {}; }
 
     std::experimental::suspend_never initial_suspend() noexcept { return {}; }