workers: Introduce a WorkerMessageFilter to ease routing/processing worker messages.

content/child/worker_thread_message_filter.cc

Index: content/child/worker_thread_message_filter.cc
diff --git a/content/child/worker_thread_message_filter.cc b/content/child/worker_thread_message_filter.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ac11a3dbd19d0eee4a71b76fecfe1e27885f87fc
--- /dev/null
+++ b/content/child/worker_thread_message_filter.cc
@@ -0,0 +1,42 @@
+// Copyright 2015 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 "content/child/worker_thread_message_filter.h"
+
+#include "base/thread_task_runner_handle.h"
+#include "content/child/thread_safe_sender.h"
+#include "content/child/worker_thread_task_runner.h"
+#include "ipc/ipc_message_macros.h"
+
+namespace content {
+
+WorkerThreadMessageFilter::WorkerThreadMessageFilter(
+    ThreadSafeSender* thread_safe_sender)
+    : main_thread_task_runner_(base::ThreadTaskRunnerHandle::Get()),
+      thread_safe_sender_(thread_safe_sender) {
+}
+
+WorkerThreadMessageFilter::~WorkerThreadMessageFilter() {
+}
+
+base::TaskRunner* WorkerThreadMessageFilter::OverrideTaskRunnerForMessage(
+    const IPC::Message& msg) {
+  if (!ShouldHandleMessage(msg))
+    return nullptr;
+  int ipc_thread_id = 0;
+  const bool success = GetWorkerThreadIdForMessage(msg, &ipc_thread_id);
+  DCHECK(success);
+  if (!ipc_thread_id)
+    return main_thread_task_runner_.get();
+  return new WorkerThreadTaskRunner(ipc_thread_id);
+}
+
+bool WorkerThreadMessageFilter::OnMessageReceived(const IPC::Message& msg) {
+  if (!ShouldHandleMessage(msg))
+    return false;
+  OnFilteredMessageReceived(msg);
+  return true;
+}
+
+}  // namespace content