[promises] port NewPromiseCapability to TF

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index f46905f7b946a6177bb203aa41fcf34aa172e960..45b8afe526da00cbeec249ae7b31455c97ffba6d 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -227,7 +227,10 @@ using v8::MemoryPressureLevel;
   V(Map, exception_map, ExceptionMap)                                          \
   V(Map, termination_exception_map, TerminationExceptionMap)                   \
   V(Map, optimized_out_map, OptimizedOutMap)                                   \
-  V(Map, stale_register_map, StaleRegisterMap)
+  V(Map, stale_register_map, StaleRegisterMap)                                 \
+  /* per-Isolate map for JSPromiseCapability. */                               \
+  /* TODO(caitp): Make this a Struct */                                        \
+  V(Map, js_promise_capability_map, JSPromiseCapabilityMap)
 
 // Entries in this list are limited to Smis and are not visited during GC.
 #define SMI_ROOT_LIST(V)                                                       \