[wasm] Rename _WASMEXP_ object to Wasm.

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.
 
 function StringRef(string) {
     this.pos = -1;
     this.string = string;
 }
 
 function DataRef(data) {
@@ skipping 341 matching lines @@
         var val = bytes[i];
         if ((typeof val) == "string") val = val.charCodeAt(0);
         view[i] = val | 0;
     }
     return buffer;
 }
 
 WasmModuleBuilder.prototype.instantiate = function(ffi, memory) {
     var buffer = this.toBuffer();
     if (memory != undefined) {
-      return _WASMEXP_.instantiateModule(buffer, ffi, memory);
+      return Wasm.instantiateModule(buffer, ffi, memory);
     } else {
-      return _WASMEXP_.instantiateModule(buffer, ffi);
+      return Wasm.instantiateModule(buffer, ffi);
     }
 }