[wasm] Implement correct 2-level namespace for imports.

test/mjsunit/wasm/stackwalk.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --expose-wasm --expose-gc --allow-natives-syntax
 
 load("test/mjsunit/wasm/wasm-constants.js");
 load("test/mjsunit/wasm/wasm-module-builder.js");
 
 function makeFFI(func) {
   var builder = new WasmModuleBuilder();
 
   var sig_index = builder.addType(kSig_i_dd);
-  builder.addImport("func", sig_index);
+  builder.addImport("mom", "func", sig_index);
   builder.addFunction("main", sig_index)
     .addBody([
       kExprGetLocal, 0,            // --
       kExprGetLocal, 1,            // --
       kExprCallFunction, 0,        // --
     ])
     .exportFunc()
 
-  return builder.instantiate({func: func}).exports.main;
+  return builder.instantiate({mom: {func: func}}).exports.main;
 }
 
 
 function makeReentrantFFI(func) {
   var main = makeFFI(reenter);
 
   function reenter(a, b) {
     print(" reenter " + a);
     if (a > 0) main(a - 1, b);
     else func();
@@ skipping 70 matching lines @@
   var gcer = builder(dogc);
   gcer(7, 7);
 
   for (var i = 0; i < 9; i++) {
     gcer(8, 8);
   }
 }
 
 runTest(makeReentrantFFI);
 runTest(makeFFI);