[wasm] Require wasm explicit asm instantiation to be of a function.

test/mjsunit/wasm/asm-wasm.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 assertWasm(expected, func, ffi) {
   print("Testing " + func.name + "...");
   assertEquals(expected, Wasm.instantiateModuleFromAsm(
       func.toString(), ffi).caller());
@@ skipping 1512 matching lines @@
       u0xffffffff: u0xffffffff,
       u0x80000000: u0x80000000,
       u0x87654321: u0x87654321,
     };
   }
   var wasm = Wasm.instantiateModuleFromAsm(asmModule.toString());
   assertEquals(0xffffffff, wasm.u0xffffffff());
   assertEquals(0x80000000, wasm.u0x80000000());
   assertEquals(0x87654321, wasm.u0x87654321());
 })();
+
+(function TestBadNoDeclaration() {
+  assertThrows(function() {
+    Wasm.instantiateModuleFromAsm('33;');
+  });
+})();
+
+(function TestBadVarDeclaration() {
+  assertThrows(function() {
+    Wasm.instantiateModuleFromAsm('var x = 3;');
+  });
+})();