[wasm] Use a Managed<WasmModule> to hold metadata about modules.

test/mjsunit/wasm/gc-buffer.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  --stress-gc --expose-gc
+
+load("test/mjsunit/wasm/wasm-constants.js");
+load("test/mjsunit/wasm/wasm-module-builder.js");
+
+function run(f) {
+  // wrap the creation in a closure so that the only thing returned is
+  // the module (i.e. the underlying array buffer of WASM wire bytes dies).
+  var module = (() => {
+    var builder = new WasmModuleBuilder();
+    builder.addImport("the_name_of_my_import", kSig_i_i);
+    builder.addFunction("main", kSig_i_i)
+      .addBody([
+        kExprGetLocal, 0,
+        kExprCallFunction, 0])
+      .exportAs("main");
+    print("module");
+    return new WebAssembly.Module(builder.toBuffer());
+  })();
+
+  gc();
+  for (var i = 0; i < 10; i++) {
+    print("  instance " + i);
+    var instance = new WebAssembly.Instance(module, {the_name_of_my_import: f});
+    var g = instance.exports.main;
+    assertEquals("function", typeof g);
+    for (var j = 0; j < 10; j++) {
+      assertEquals(f(j), g(j));
+    }
+  }
+}
+
+(function test() {
+  for (var i = 0; i < 3; i++) {
+    run(x => (x + 19));
+    run(x => (x - 18));
+  }
+})();