[wasm] Support a two-level namespace for imports.

test/mjsunit/wasm/test-wasm-module-builder.js

 // Copyright 2016 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
 
 load('test/mjsunit/wasm/wasm-constants.js');
 load('test/mjsunit/wasm/wasm-module-builder.js');
 
 var debug = false;
@@ skipping 120 matching lines @@
     for (var i = 0; i < whole.byteLength; i++) {
       whole[i] = 0xff;
     }
     var array2 = new Uint8Array(buffer2, kPad, buffer.byteLength);
     for (var i = 0; i < array2.byteLength; i++) {
       array2[i] = array[i];
     }
     var instance = Wasm.instantiateModule(array2);
     assertEquals(17, instance.exports.blarg());
 })();
+
+(function ImportTestTwoLevel() {
+    var module = new WasmModuleBuilder();
+    var index = module.addImportWithModule("mod", "print", [kAstStmt, kAstI32]);
+    module.addFunction("foo", [kAstStmt])
+        .addBody([kExprCallImport, index, kExprI8Const, 19])
+        .exportAs("main");
+
+    var buffer = module.toBuffer(debug);
+    var instance = Wasm.instantiateModule(buffer, {mod: {print: print}});
+    print("should print 19! ");
+    instance.exports.main();
+})();