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

test/mjsunit/wasm/stackwalk.js

Index: test/mjsunit/wasm/stackwalk.js
diff --git a/test/mjsunit/wasm/stackwalk.js b/test/mjsunit/wasm/stackwalk.js
index cd560ec62bc709f7e9f21100f68cee989a084a30..d2810fce459d3b23c4acb4b7dd28beaae1997b77 100644
--- a/test/mjsunit/wasm/stackwalk.js
+++ b/test/mjsunit/wasm/stackwalk.js
@@ -11,7 +11,7 @@ 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,            // --
@@ -20,7 +20,7 @@ function makeFFI(func) {
     ])
     .exportFunc()
 
-  return builder.instantiate({func: func}).exports.main;
+  return builder.instantiate({mom: {func: func}}).exports.main;
 }