Add WorkerSettings to expose certain flag values in WorkerGlobalScope

third_party/WebKit/Source/core/workers/WorkerSettings.cpp

+// Copyright 2016 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 "core/workers/WorkerSettings.h"
+
+#include "core/workers/WorkerGlobalScope.h"
+
+namespace blink {
+
+const char* WorkerSettings::supplementName()
+{
+    return "WorkerSettings";
+}
+
+WorkerSettings* WorkerSettings::create(Settings* settings)
+{
+    WorkerSettings* workerSettings = new WorkerSettings();
+    workerSettings->copyFlagValuesFromSettings(settings);
+    return workerSettings;
+}
+
+WorkerSettings* WorkerSettings::from(ExecutionContext* context)

[kinuko, 2016/07/22 09:02:54]

I'm not sure if we should pass this as a supplement of WorkerClients.  It's
handy to pass things from main thread to worker thread, but Settings isn't a
client, and isn't something that's particularly about a specific module. It
needs a little more plumbing but we could probably just pass it directly via
WorkerThreadStartupData?

[xlai (Olivia), 2016/07/22 21:53:30]

I did think of making WorkerSetting to become a member
in WorkerThreadStartupData but was wondering how the workers
team think about the design. The structure is actually simpler.

Also, if WorkerSetting becomes a member in WorkerThreadStartupData.
How do I make sure that the flag values stored in WorkerSetting
remain unchanged when the StartupData is passed from main
to worker thread? Will just doing release() on std::unique_ptr work? 

[nhiroki, 2016/07/25 11:14:48]

I'd prefer to pass it via WorkerThreadStartupData. It'd be more straightforward.
Could you explain what you're concerned a little more specifically? I'm not sure
who may change the flag values during the period.

In my understanding, WorkerThreadStartupData approach is done as follows:

1) copy flag values from Settings to WorkerSettings on main thread.
2) create WorkerThreadStartupData and make it own the worker settings on main
thread.
3) post the startup data with its ownership from main thread to worker thread
(see WorkerThread::start())
4) WorkerGlobalScope receives the passed settings and owns it on worker thread.

At the step 4, the flag values should not be changed from the step 1.

+{
+    if (context->isWorkerGlobalScope()) {
+        WorkerClients* clients = toWorkerGlobalScope(*context).clients();
+        DCHECK(clients);
+        return static_cast<WorkerSettings*>(Supplement<WorkerClients>::from(clients, supplementName()));
+    }
+    return nullptr;
+}
+
+void WorkerSettings::copyFlagValuesFromSettings(Settings* settings)
+{
+    m_disableReadingFromCanvas = settings->disableReadingFromCanvas();
+}
+
+void provideWorkerSettingsToWorker(WorkerClients* clients, WorkerSettings* client)
+{
+    clients->provideSupplement(WorkerSettings::supplementName(), client);
+}
+
+DEFINE_TRACE(WorkerSettings)
+{
+    Supplement<WorkerClients>::trace(visitor);
+}
+}

[kinuko, 2016/07/22 09:02:54]

ditto

[xlai (Olivia), 2016/07/22 21:53:30]

Done.