Remove redundant DevToolsManager methods and clean up its clients.

content/browser/devtools/devtools_agent_host_impl.cc

Index: content/browser/devtools/devtools_agent_host_impl.cc
diff --git a/content/browser/devtools/devtools_agent_host_impl.cc b/content/browser/devtools/devtools_agent_host_impl.cc
index a0f337a7ed546ac2e49ddd7dcfcb6dd93f075a30..881e4bfcf04bd9379636321d08720fe16ed218d8 100644
--- a/content/browser/devtools/devtools_agent_host_impl.cc
+++ b/content/browser/devtools/devtools_agent_host_impl.cc
@@ -9,6 +9,7 @@
 #include "base/basictypes.h"
 #include "base/guid.h"
 #include "base/lazy_instance.h"
+#include "content/browser/devtools/devtools_manager_impl.h"
 
 namespace content {
 
@@ -37,6 +38,10 @@ scoped_refptr<DevToolsAgentHost> DevToolsAgentHost::GetForId(
   return it->second;
 }
 
+bool DevToolsAgentHostImpl::IsAttached() {
+  return !!DevToolsManagerImpl::GetInstance()->GetDevToolsClientHostFor(this);
+}
+
 void DevToolsAgentHostImpl::InspectElement(int x, int y) {
 }