Implement WebThreadSupportingGC, which wraps a WebThread attached to Oilpan's GC

Source/platform/WebThreadRunner.cpp

Index: Source/platform/WebThreadRunner.cpp
diff --git a/Source/platform/WebThreadRunner.cpp b/Source/platform/WebThreadRunner.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..88264dbd318d5a77fd14552d6bd3e755d0c363c8
--- /dev/null
+++ b/Source/platform/WebThreadRunner.cpp
@@ -0,0 +1,38 @@
+// Copyright 2014 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 "config.h"
+#include "platform/WebThreadRunner.h"
+
+namespace blink {
+
+PassOwnPtr<WebThreadRunner> WebThreadRunner::create(const char* name)
+{
+    return adoptPtr(new WebThreadRunner(name));
+}
+
+WebThreadRunner::WebThreadRunner(const char* name)
+    : m_thread(adoptPtr(blink::Platform::current()->createThread(name)))
+{
+}
+
+void WebThreadRunner::attachGC()
+{
+    m_pendingGCRunner = adoptPtr(new PendingGCRunner);
+    m_messageLoopInterruptor = adoptPtr(new MessageLoopInterruptor(&platformThread()));
+    platformThread().addTaskObserver(m_pendingGCRunner.get());
+    ThreadState::attach();
+    ThreadState::current()->addInterruptor(m_messageLoopInterruptor.get());
+}
+
+void WebThreadRunner::detachGC()
+{
+    ThreadState::current()->removeInterruptor(m_messageLoopInterruptor.get());
+    ThreadState::detach();
+    platformThread().removeTaskObserver(m_pendingGCRunner.get());
+    m_pendingGCRunner = nullptr;
+    m_messageLoopInterruptor = nullptr;
+}
+
+} // namespace blink