[Worklets] Add basic debugging to main thread worklets.

third_party/WebKit/Source/core/workers/MainThreadWorkletGlobalScope.h

+// 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.
+
+#ifndef MainThreadWorkletGlobalScope_h
+#define MainThreadWorkletGlobalScope_h
+
+#include "core/dom/ExecutionContext.h"
+#include "core/frame/LocalFrameLifecycleObserver.h"
+#include "core/workers/WorkerOrWorkletGlobalScope.h"
+
+namespace blink {
+
+class LocalFrame;
+
+class CORE_EXPORT MainThreadWorkletGlobalScope : public WorkerOrWorkletGlobalScope, public LocalFrameLifecycleObserver {

[ikilpatrick, 2016/03/09 18:40:26]

Instead of inheriting from LocalFrameLifecycleObserver, this could just expose a
pure virtual fn:
virtual LocalFrame* frame() const = 0;

But still needs to inherit from WorkerOrWorkletGlobalScope to have
toMainThreadWorkletGlobalScope type conversion.
Up to you.

Not tied to name at all :)

+public:
+    DEFINE_INLINE_VIRTUAL_TRACE()
+    {
+        WorkerOrWorkletGlobalScope::trace(visitor);
+        LocalFrameLifecycleObserver::trace(visitor);
+    }
+
+protected:
+    explicit MainThreadWorkletGlobalScope(LocalFrame* frame)
+        : LocalFrameLifecycleObserver(frame) { }
+};
+
+DEFINE_TYPE_CASTS(MainThreadWorkletGlobalScope, ExecutionContext, context, context->isWorkletGlobalScope(), context.isWorkletGlobalScope());
+
+} // namespace blink
+
+#endif // MainThreadWorkletGlobalScope_h