DevTools: prepare workers for DevToolsManager::Attach(Detach)ClientHost removal.

content/browser/devtools/devtools_agent_host.cc

Index: content/browser/devtools/devtools_agent_host.cc
diff --git a/content/browser/devtools/devtools_agent_host.cc b/content/browser/devtools/devtools_agent_host.cc
index fa5bc0e75e90d2e9624f5d66b3124bdfeb3f4af4..1362891c490754eea23a9af6903e1c920913537b 100644
--- a/content/browser/devtools/devtools_agent_host.cc
+++ b/content/browser/devtools/devtools_agent_host.cc
@@ -47,11 +47,13 @@ void DevToolsAgentHost::AddMessageToConsole(ConsoleMessageLevel level,
       message));
 }
 
-void DevToolsAgentHost::NotifyCloseListener() {
+bool DevToolsAgentHost::NotifyCloseListener() {
   if (close_listener_) {
     close_listener_->AgentHostClosing(this);
     close_listener_ = NULL;
+    return true;
   }
+  return false;
 }
 
 }  // namespace content