Implement rudimentary module linking.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index d1cdda03b18c8ad8a0a8cd9d7df8e30259d33eb5..af86f44ad2588677c3140270b2c0512c6247799c 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -529,6 +529,8 @@ class Heap {
   MUST_USE_RESULT MaybeObject* AllocateJSObject(
       JSFunction* constructor, PretenureFlag pretenure = NOT_TENURED);
 
+  MUST_USE_RESULT MaybeObject* AllocateJSModule();
+
   // Allocate a JSArray with no elements
   MUST_USE_RESULT MaybeObject* AllocateEmptyJSArray(
       ElementsKind elements_kind,
@@ -820,6 +822,10 @@ class Heap {
   // Allocate a global (but otherwise uninitialized) context.
   MUST_USE_RESULT MaybeObject* AllocateGlobalContext();
 
+  // Allocate a module context.
+  MUST_USE_RESULT MaybeObject* AllocateModuleContext(Context* previous,
+                                                     ScopeInfo* scope_info);
+
   // Allocate a function context.
   MUST_USE_RESULT MaybeObject* AllocateFunctionContext(int length,
                                                        JSFunction* function);