compositor-worker: Initialize CW machinery plumbing to compositor and fire CW rAF callbacks.

third_party/WebKit/Source/web/CompositorProxyClientImpl.h

+// 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.
+
+#ifndef CompositorProxyClientImpl_h
+#define CompositorProxyClientImpl_h
+
+#include "core/dom/CompositorProxyClient.h"
+#include "wtf/Noncopyable.h"
+
+namespace blink {
+
+class CompositorMutatorImpl;
+class CompositorWorkerGlobalScope;
+class WorkerGlobalScope;
+
+// Mediates between one CompositorWorkerGlobalScope and the associated CompositorMutatorImpl.
+// There is one CompositorProxyClientImpl per worker but there may be multiple for a given
+// mutator, e.g. if a single document creates multiple CompositorWorker objects.
+//
+// Should be accessed only on the compositor thread.
+class CompositorProxyClientImpl final : public GarbageCollected<CompositorProxyClientImpl>, public CompositorProxyClient {
+    USING_GARBAGE_COLLECTED_MIXIN(CompositorProxyClientImpl);
+    WTF_MAKE_NONCOPYABLE(CompositorProxyClientImpl);
+public:
+    CompositorProxyClientImpl(CompositorMutatorImpl*);
+    DECLARE_VIRTUAL_TRACE();
+
+    // Runs the animation frame callback for the frame starting at the given time.
+    // Returns true if another animation frame was requested (i.e. should be reinvoked next frame).
+    bool mutate(double monotonicTimeNow);
+
+    // CompositorProxyClient:
+    void setGlobalScope(WorkerGlobalScope*) override;
+    void requestAnimationFrame() override;
+
+private:
+    bool executeAnimationFrameCallbacks(double monotonicTimeNow);
+
+    WeakMember<CompositorMutatorImpl> m_mutator;

[jbroman, 2016/05/04 17:59:00]

Should this be a weak member? It's used without null checking, so I'd have
expected this to be a strong Member<CompositorMutatorImpl>.

WeakMember says to me that it's possible for this object to still be alive when
the pointee is gone, but if so it should handle that.

The Oilpan docs suggest preferring Member:
"The use of WeakMember<T> incurs some overhead in garbage collector’s
performance. ... More specifically, WeakMember<T> should be used only if the
owner of a weak member can outlive the pointed object. Otherwise, Member<T>
should be used."
https://chromium.googlesource.com/chromium/src/+/master/third_party/WebKit/So...

[flackr, 2016/05/04 21:52:41]

Seems fine to me, this should definitely be gone before the
CompositorMutatorImpl. Done.

+
+    WeakMember<CompositorWorkerGlobalScope> m_globalScope;

[jbroman, 2016/05/04 17:59:00]

Writing the above comment has made me wonder whether this needs to be weak or
not, as well.

[flackr, 2016/05/04 21:52:41]

Done. This doesn't need to be weak either. In fact, since this is destructed
together with the global scope and doesn't need to remove itself from the
CompositorMutatorImpl, CompositorWorkerGlobalScope no longer needs the
finalizer. Removed the finalizer there and verified that everything destructs as
expected.

+    bool m_requestedAnimationFrameCallbacks;
+};
+
+} // namespace blink
+
+#endif // CompositorProxyClientImpl_h