[Gin] Add Arguments::GetHolderCreationContext()

Currently, in order to get at the creation context of the holder, one
has to do the following:
v8::Local<v8::Object> holder;
arguments->GetHolder(&holder);
v8::Local<v8::Context> context = holder->CreationContext();

This isn't terrible, but it's a little verbose when all we really want
is FunctionCallbackInfo::Holder::CreationContext(). Add a method to get
at it directly.

BUG=None

Review-Url: https://codereview.chromium.org/2765853004
Cr-Commit-Position: refs/heads/master@{#459251}

extensions/renderer/chrome_setting.cc

@@ -104,10 +104,7 @@ void ChromeSetting::Get(gin::Arguments* arguments) {
 void ChromeSetting::Set(gin::Arguments* arguments) {
   v8::Isolate* isolate = arguments->isolate();
   v8::HandleScope handle_scope(isolate);
-
-  v8::Local<v8::Object> holder;
-  CHECK(arguments->GetHolder(&holder));
-  v8::Local<v8::Context> context = holder->CreationContext();
+  v8::Local<v8::Context> context = arguments->GetHolderCreationContext();
 
   v8::Local<v8::Value> value = arguments->PeekNext();
   // The set schema included in the Schema object is generic, since it varies
@@ -129,9 +126,7 @@ void ChromeSetting::Clear(gin::Arguments* arguments) {
 v8::Local<v8::Value> ChromeSetting::GetOnChangeEvent(
     gin::Arguments* arguments) {
   v8::Isolate* isolate = arguments->isolate();
-  v8::Local<v8::Object> holder;
-  CHECK(arguments->GetHolder(&holder));
-  v8::Local<v8::Context> context = holder->CreationContext();
+  v8::Local<v8::Context> context = arguments->GetHolderCreationContext();
   v8::Local<v8::Object> wrapper = GetWrapper(isolate);
   v8::Local<v8::Private> key = v8::Private::ForApi(
       isolate, gin::StringToSymbol(isolate, "onChangeEvent"));
@@ -161,9 +156,7 @@ void ChromeSetting::HandleFunction(const std::string& method_name,
                                    gin::Arguments* arguments) {
   v8::Isolate* isolate = arguments->isolate();
   v8::HandleScope handle_scope(isolate);
-  v8::Local<v8::Object> holder;
-  CHECK(arguments->GetHolder(&holder));
-  v8::Local<v8::Context> context = holder->CreationContext();
+  v8::Local<v8::Context> context = arguments->GetHolderCreationContext();
 
   std::vector<v8::Local<v8::Value>> argument_list;
   if (arguments->Length() > 0) {

gin/BUILD.gn

@@ -159,6 +159,7 @@ source_set("gin_test") {
 
 test("gin_unittests") {
   sources = [
+    "arguments_unittest.cc",
     "converter_unittest.cc",
     "interceptor_unittest.cc",
     "modules/module_registry_unittest.cc",

gin/arguments.cc

@@ -32,6 +32,10 @@ v8::Local<v8::Value> Arguments::PeekNext() const {
   return (*info_)[next_];
 }
 
+v8::Local<v8::Context> Arguments::GetHolderCreationContext() {
+  return info_->Holder()->CreationContext();
+}
+
 std::string V8TypeAsString(v8::Local<v8::Value> value) {
   if (value.IsEmpty())
     return "<empty handle>";

gin/arguments.h

@@ -74,6 +74,9 @@ class GIN_EXPORT Arguments {
     info_->GetReturnValue().Set(v8_value);
   }
 
+  // Returns the creation context of the Holder.
+  v8::Local<v8::Context> GetHolderCreationContext();
+
   // Always check the return value whether the handle is empty before
   // dereferencing the handle.
   v8::Local<v8::Value> PeekNext() const;

gin/arguments_unittest.cc

@@ -0,0 +1,67 @@
+// Copyright 2017 The Chromium 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 "gin/arguments.h"
+
+#include "base/bind.h"
+#include "gin/converter.h"
+#include "gin/object_template_builder.h"
+#include "gin/public/isolate_holder.h"
+#include "gin/test/v8_test.h"
+#include "v8/include/v8.h"
+
+namespace gin {
+
+using ArgumentsTest = V8Test;
+
+// Test that Arguments::GetHolderCreationContext returns the proper context.
+TEST_F(ArgumentsTest, TestArgumentsHolderCreationContext) {
+  v8::Isolate* isolate = instance_->isolate();
+  v8::HandleScope handle_scope(isolate);
+
+  v8::Local<v8::Context> creation_context = context_.Get(instance_->isolate());
+
+  auto check_creation_context = [](v8::Local<v8::Context> expected_context,
+                                   gin::Arguments* arguments) {
+    EXPECT_EQ(expected_context, arguments->GetHolderCreationContext());
+  };
+
+  // Create an object that will compare GetHolderCreationContext() with
+  // |creation_context|.
+  v8::Local<v8::ObjectTemplate> object_template =
+      ObjectTemplateBuilder(isolate)
+          .SetMethod("checkCreationContext",
+                     base::Bind(check_creation_context, creation_context))
+          .Build();
+
+  v8::Local<v8::Object> object =
+      object_template->NewInstance(creation_context).ToLocalChecked();
+
+  // Call checkCreationContext() on the generated object using the passed-in
+  // context as the current context.
+  auto test_context = [object, isolate](v8::Local<v8::Context> context) {
+    v8::Context::Scope context_scope(context);
+    const char kCallFunction[] = "(function(o) { o.checkCreationContext(); })";
+    v8::Local<v8::Script> script =
+        v8::Script::Compile(context, StringToV8(isolate, kCallFunction))
+            .ToLocalChecked();
+    v8::Local<v8::Function> function;
+    ASSERT_TRUE(ConvertFromV8(isolate, script->Run(), &function));
+    v8::Local<v8::Value> args[] = {object};
+    function->Call(v8::Undefined(isolate), arraysize(args), args);
+  };
+
+  // Test calling in the creation context.
+  test_context(creation_context);
+
+  {
+    // Create a second context, and test calling in that. The creation context
+    // should be the same (even though the current context has changed).
+    v8::Local<v8::Context> second_context =
+        v8::Context::New(isolate, nullptr, v8::Local<v8::ObjectTemplate>());
+    test_context(second_context);
+  }
+}
+
+}  // namespace gin