[wasm][asm.js] Ignore duplicate exports in asm.js.

test/mjsunit/asm/asm-validation.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: --validate-asm --allow-natives-syntax
 
 // Note that this test file contains tests that explicitly check modules are
 // valid asm.js and then break them with invalid instantiation arguments. If
 // this script is run more than once (e.g. --stress-opt) then modules remain
 // broken in the second run and assertions would fail. We prevent re-runs.
@@ skipping 298 matching lines @@
       x = x | true;
       return x;
     }
     return { foo: foo };
   }
   var m = Module();
   assertFalse(%IsAsmWasmCode(Module));
   assertEquals(3, m.foo(3));
 })();
 
+(function TestBadExportTwice() {
+  function Module() {
+    "use asm";
+    function bar() { return 1; }
+    function baz() { return 2; }
+    return {foo: bar, foo: baz};
+  }
+  var m = Module();
+  assertTrue(%IsAsmWasmCode(Module));
+  assertEquals(2, m.foo());
+})();
+
 (function TestBadImport() {
   function Module(stdlib) {
     "use asm";
     var set = 0;
     var foo = stdlib[set];
     return {};
   }
   var m = Module(this);
   assertFalse(%IsAsmWasmCode(Module));
 })();
@@ skipping 27 matching lines @@
           return 43;
       }
       return 0;
     }
     return { foo: foo };
   }
   var m = Module();
   assertFalse(%IsAsmWasmCode(Module));
   assertEquals(43, m.foo(3));
 })();