[wasm] Fix bug with empty input to Wasm.instantiateModuleFromAsm()

R=ahaas@chromium.org,bradnelson@chromium.org
BUG=chromium:605488
LOG=Y

Review-Url: https://codereview.chromium.org/1940243002
Cr-Commit-Position: refs/heads/master@{#35974}

src/wasm/wasm-js.cc

@@ -134,6 +134,11 @@ v8::internal::wasm::WasmModuleIndex* TranslateAsmModule(
     return nullptr;
   }
 
+  if (info->scope()->declarations()->length() == 0) {
+    thrower->Error("Asm.js validation failed: no declarations in scope");
+    return nullptr;
+  }
+
   info->set_literal(
       info->scope()->declarations()->at(0)->AsFunctionDeclaration()->fun());
 

test/mjsunit/regress/regress-605488.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
+
+try {
+  Wasm.instantiateModuleFromAsm("");
+  assertTrue(false);
+} catch (e) {
+  print("Caught: " + e);
+}