[wasm] Support undefined indirect table entries, behind a flag.

test/mjsunit/wasm/wasm-constants.js

 // Copyright 2015 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
 
 function bytes() {
   var buffer = new ArrayBuffer(arguments.length);
   var view = new Uint8Array(buffer);
   for (var i = 0; i < arguments.length; i++) {
@@ skipping 285 matching lines @@
 var kExprI64Rol = 0xb9;
 
 var kTrapUnreachable          = 0;
 var kTrapMemOutOfBounds       = 1;
 var kTrapDivByZero            = 2;
 var kTrapDivUnrepresentable   = 3;
 var kTrapRemByZero            = 4;
 var kTrapFloatUnrepresentable = 5;
 var kTrapFuncInvalid          = 6;
 var kTrapFuncSigMismatch      = 7;
+var kTrapDefaultFuncCall      = 8;
 
 var kTrapMsgs = [
   "unreachable",
   "memory access out of bounds",
   "divide by zero",
   "divide result unrepresentable",
   "remainder by zero",
   "integer result unrepresentable",
   "invalid function",
-  "function signature mismatch"
+  "function signature mismatch",
+  "default function call"
 ];
 
 function assertTraps(trap, code) {
     var threwException = true;
     try {
       if (typeof code === 'function') {
         code();
       } else {
         eval(code);
       }
       threwException = false;
     } catch (e) {
       assertEquals("object", typeof e);
       assertEquals(kTrapMsgs[trap], e.message);
       // Success.
       return;
     }
     throw new MjsUnitAssertionError("Did not trap, expected: " + kTrapMsgs[trap]);
 }