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

test/mjsunit/wasm/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.
 
 // Used for encoding f32 and double constants to bits.
 let __buffer = new ArrayBuffer(8);
 let byte_view = new Int8Array(__buffer);
 let f32_view = new Float32Array(__buffer);
 let f64_view = new Float64Array(__buffer);
 
@@ skipping 161 matching lines @@
   }
 
   addFunction(name, type) {
     let type_index = (typeof type) == "number" ? type : this.addType(type);
     let func = new WasmFunctionBuilder(this, name, type_index);
     func.index = this.functions.length + this.num_imported_funcs;
     this.functions.push(func);
     return func;
   }
 
-  addImportWithModule(module, name, type) {
+  addImport(module = "", name, type) {
     let type_index = (typeof type) == "number" ? type : this.addType(type);
     this.imports.push({module: module, name: name, kind: kExternalFunction,
                        type: type_index});
     return this.num_imported_funcs++;
   }
 
-  addImport(name, type) {
-    return this.addImportWithModule(name, undefined, type);
-  }
-
-  addImportedGlobal(module, name, type) {
+  addImportedGlobal(module = "", name, type) {
     let o = {module: module, name: name, kind: kExternalGlobal, type: type,
              mutable: false}
     this.imports.push(o);
     return this.num_imported_globals++;
   }
 
-  addImportedMemory(module, name, initial = 0, maximum) {
+  addImportedMemory(module = "", name, initial = 0, maximum) {
     let o = {module: module, name: name, kind: kExternalMemory,
              initial: initial, maximum: maximum};
     this.imports.push(o);
     return this;
   }
 
-  addImportedTable(module, name, initial, maximum) {
+  addImportedTable(module = "", name, initial, maximum) {
     let o = {module: module, name: name, kind: kExternalTable, initial: initial,
              maximum: maximum};
     this.imports.push(o);
   }
 
   addExport(name, index) {
     this.exports.push({name: name, kind: kExternalFunction, index: index});
     return this;
   }
 
@@ skipping 332 matching lines @@
     }
     return buffer;
   }
 
   instantiate(...args) {
     let module = new WebAssembly.Module(this.toBuffer());
     let instance = new WebAssembly.Instance(module, ...args);
     return instance;
   }
 }