[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 6e5d788bd1d3644b0d0deb13a8f117ab63c91c42..b370a365d6c03441aec97a3247b55494f5decff2 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)                                                       \