Introduce AnimationWorkletProxyClient and necessary plumbing to get it in worklet messaging proxy.

third_party/WebKit/Source/web/AnimationWorkletProxyClientImpl.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 "web/AnimationWorkletProxyClientImpl.h"
+
+#include "core/dom/CompositorProxy.h"
+#include "platform/graphics/CompositorMutableStateProvider.h"
+#include "web/CompositorMutatorImpl.h"
+
+namespace blink {
+
+AnimationWorkletProxyClientImpl::AnimationWorkletProxyClientImpl(
+    CompositorMutatorImpl* mutator)
+    : m_mutator(mutator) {
+  DCHECK(isMainThread());
+}
+
+DEFINE_TRACE(AnimationWorkletProxyClientImpl) {
+  visitor->trace(m_proxies);
+  AnimationWorkletProxyClient::trace(visitor);
+  CompositorAnimator::trace(visitor);
+}
+
+bool AnimationWorkletProxyClientImpl::mutate(
+    double monotonicTimeNow,
+    CompositorMutableStateProvider* provider) {
+  DCHECK(!isMainThread());
+  // TODO(majidvp): actually call JS |animate| callbacks.
+
+  // Always request another rAF for now.
+  return true;
+}
+
+void AnimationWorkletProxyClientImpl::registerCompositorProxy(
+    CompositorProxy* proxy) {
+  DCHECK(!isMainThread());
+  m_proxies.add(proxy);
+}
+
+void AnimationWorkletProxyClientImpl::unregisterCompositorProxy(
+    CompositorProxy* proxy) {
+  DCHECK(!isMainThread());
+  m_proxies.remove(proxy);
+}
+
+}  // namespace blink