[wasm] Names of exported functions should be the stringified function index.

test/mjsunit/wasm/function-prototype.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");
 
 (function TestFunctionPrototype() {
   var builder = new WasmModuleBuilder();
 
-  builder.addFunction("nine", kSig_i_v)
+  var f = builder.addFunction("nine", kSig_i_v)
     .addBody([kExprI8Const, 9])
     .exportFunc();
 
   var func = builder.instantiate().exports.nine;
 
   // Check type and existence of prototype
   assertEquals("function", typeof func.apply);
   assertTrue(func.prototype != undefined);
-  assertEquals("nine", func.name);
+  assertEquals(String(f.index), func.name);
   assertEquals(undefined, func.displayName);
 
   // Check that .apply() works.
   assertEquals(9, func.apply([]));
   assertEquals(9, func.apply([1]));
   assertEquals(9, func.apply([2, 3]));
   assertEquals(9, func.apply([6, 7, 9, 9]));
 
   // TODO(titzer): assertEquals(1, func.length);
 
   // Check we don't crash when converting to a string.
   print(func.toString());
 })();