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

src/wasm/wasm-js.cc

 // 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.
 
 #include "src/api.h"
 #include "src/api-natives.h"
 #include "src/assert-scope.h"
 #include "src/ast/ast.h"
 #include "src/ast/scopes.h"
 #include "src/factory.h"
@@ skipping 116 matching lines @@
     i::ParseInfo* info, i::Handle<i::Object> foreign, ErrorThrower* thrower) {
   info->set_global();
   info->set_lazy(false);
   info->set_allow_lazy_parsing(false);
   info->set_toplevel(true);
 
   if (!i::Compiler::ParseAndAnalyze(info)) {
     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());
 
   v8::internal::AsmTyper typer(info->isolate(), info->zone(), *(info->script()),
                                info->literal());
   if (i::FLAG_enable_simd_asmjs) {
     typer.set_allow_simd(true);
   }
   if (!typer.Validate()) {
     thrower->Error("Asm.js validation failed: %s", typer.error_message());
@@ skipping 179 matching lines @@
     int unused_property_fields = in_object_properties - pre_allocated;
     Handle<Map> map = Map::CopyInitialMap(
         prev_map, instance_size, in_object_properties, unused_property_fields);
 
     context->set_wasm_function_map(*map);
   }
 }
 
 }  // namespace internal
 }  // namespace v8