Don't expose a LayerImpl reference to CompositorProxy.

third_party/WebKit/Source/web/CompositorWorkerProxyClientImpl.cpp

Index: third_party/WebKit/Source/web/CompositorWorkerProxyClientImpl.cpp
diff --git a/third_party/WebKit/Source/web/CompositorWorkerProxyClientImpl.cpp b/third_party/WebKit/Source/web/CompositorWorkerProxyClientImpl.cpp
index c564b861cb89f47fc1470e1b1f228a0ccf242fb3..cbc4bc5ff5561f2abd06b497235734a596708bce 100644
--- a/third_party/WebKit/Source/web/CompositorWorkerProxyClientImpl.cpp
+++ b/third_party/WebKit/Source/web/CompositorWorkerProxyClientImpl.cpp
@@ -27,7 +27,7 @@ class ScopedCompositorMutableState final {
       : m_proxies(proxies) {
     for (CompositorProxy* proxy : m_proxies) {
       proxy->takeCompositorMutableState(
-          stateProvider->getMutableStateFor(proxy->elementId()));
+          stateProvider->getMutableStateFor(proxy->proxyId()));
     }
   }
   ~ScopedCompositorMutableState() {
@@ -112,11 +112,17 @@ bool CompositorWorkerProxyClientImpl::executeAnimationFrameCallbacks(
 
 void CompositorWorkerProxyClientImpl::registerCompositorProxy(
     CompositorProxy* proxy) {
+  TRACE_EVENT0("compositor-worker",
+               "CompositorWorkerProxyClientImpl::registerCompositorProxy");
+  m_mutator->registerCompositorProxy(proxy);
   m_proxies.insert(proxy);
 }
 
 void CompositorWorkerProxyClientImpl::unregisterCompositorProxy(
     CompositorProxy* proxy) {
+  TRACE_EVENT0("compositor-worker",
+               "CompositorWorkerProxyClientImpl::unregisterCompositorProxy");
+  m_mutator->registerCompositorProxy(proxy);
   m_proxies.erase(proxy);
 }