Implement rudimentary module linking.

src/scopes.cc

Index: src/scopes.cc
diff --git a/src/scopes.cc b/src/scopes.cc
index 80c7eb2ae93bd8f49d8d885f4976c11c4229c620..7f663fd18e50736e41b5fd8c531d8dac434a89e8 100644
--- a/src/scopes.cc
+++ b/src/scopes.cc
@@ -1091,7 +1091,7 @@ bool Scope::MustAllocateInContext(Variable* var) {
   // Exceptions: temporary variables are never allocated in a context;
   // catch-bound variables are always allocated in a context.
   if (var->mode() == TEMPORARY) return false;
-  if (is_catch_scope() || is_block_scope()) return true;
+  if (is_catch_scope() || is_block_scope() || is_module_scope()) return true;
   return var->has_forced_context_allocation() ||
       scope_calls_eval_ ||
       inner_scope_calls_eval_ ||
@@ -1235,7 +1235,8 @@ void Scope::AllocateVariablesRecursively() {
   // Force allocation of a context for this scope if necessary. For a 'with'
   // scope and for a function scope that makes an 'eval' call we need a context,
   // even if no local variables were statically allocated in the scope.
-  bool must_have_context = is_with_scope() ||
+  // Likewise for modules.
+  bool must_have_context = is_with_scope() || is_module_scope() ||
       (is_function_scope() && calls_eval());
 
   // If we didn't allocate any locals in the local context, then we only