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

test/mjsunit/wasm/stack.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.
 
 // clang-format off
 // Flags: --expose-wasm
 
 load("test/mjsunit/wasm/wasm-constants.js");
 load("test/mjsunit/wasm/wasm-module-builder.js");
 
@@ skipping 24 matching lines @@
 
 
 var stack;
 function STACK() {
   var e = new Error();
   stack = e.stack;
 }
 
 var builder = new WasmModuleBuilder();
 
-builder.addImport("func", kSig_v_v);
+builder.addImport("mod", "func", kSig_v_v);
 
 builder.addFunction("main", kSig_v_v)
   .addBody([kExprCallFunction, 0])
   .exportAs("main");
 
 builder.addFunction("exec_unreachable", kSig_v_v)
   .addBody([kExprUnreachable])
   .exportAs("exec_unreachable");
 
 // Make this function unnamed, just to test also this case.
 var mem_oob_func = builder.addFunction(undefined, kSig_i_v)
   // Access the memory at offset -1, to provoke a trap.
   .addBody([kExprI32Const, 0x7f, kExprI32LoadMem8S, 0, 0])
   .exportAs("mem_out_of_bounds");
 
 // Call the mem_out_of_bounds function, in order to have two WASM stack frames.
 builder.addFunction("call_mem_out_of_bounds", kSig_i_v)
   .addBody([kExprCallFunction, mem_oob_func.index])
   .exportAs("call_mem_out_of_bounds");
 
-var module = builder.instantiate({func: STACK});
+var module = builder.instantiate({mod: {func: STACK}});
 
 (function testSimpleStack() {
   var expected_string = "Error\n" +
     // The line numbers below will change as this test gains / loses lines..
     "    at STACK (stack.js:39:11)\n" +           // --
     "    at main (<WASM>[1]+1)\n" +               // --
     "    at testSimpleStack (stack.js:76:18)\n" + // --
     "    at stack.js:78:3";                       // --
 
   module.exports.main();
@@ skipping 63 matching lines @@
     .exportFunc()
   builder.appendToTable([0]);
 
   try {
     builder.instantiate().exports.recursion();
     fail("expected wasm exception");
   } catch (e) {
     assertEquals("Maximum call stack size exceeded", e.message, "trap reason");
   }
 })();