Devtools[LayoutEditor]: Pass data about property change from InspectorOverlayPage

Source/web/WebDevToolsAgentImpl.cpp

Index: Source/web/WebDevToolsAgentImpl.cpp
diff --git a/Source/web/WebDevToolsAgentImpl.cpp b/Source/web/WebDevToolsAgentImpl.cpp
index ec6e783c20b684303dc7e686d0601f96287005fc..1ad2b00ed831ae4317b86b55be2fd99344272c1d 100644
--- a/Source/web/WebDevToolsAgentImpl.cpp
+++ b/Source/web/WebDevToolsAgentImpl.cpp
@@ -490,6 +490,7 @@ void WebDevToolsAgentImpl::attach(const WebString& hostId)
 
     initializeDeferredAgents();
     m_resourceAgent->setHostId(hostId);
+    m_overlay->setCSSAgent(m_cssAgent.get());
 
     m_inspectorFrontend = adoptPtr(new InspectorFrontend(this));
     // We can reconnect to existing front-end -> unmute state.
@@ -533,6 +534,7 @@ void WebDevToolsAgentImpl::detach()
 
     // Release overlay resources.
     m_overlay->clear();
+    m_overlay->setCSSAgent(nullptr);
     InspectorInstrumentation::frontendDeleted();
     InspectorInstrumentation::unregisterInstrumentingAgents(m_instrumentingAgents.get());