Remove redundant DevToolsManager methods and clean up its clients.

content/browser/devtools/devtools_external_agent_proxy_impl.cc

Index: content/browser/devtools/devtools_external_agent_proxy_impl.cc
diff --git a/content/browser/devtools/devtools_external_agent_proxy_impl.cc b/content/browser/devtools/devtools_external_agent_proxy_impl.cc
index 0d77b53a33b79bc941d5f4ef555ee1f22a8b17d0..d5cb741d4a6dbad93897c93833d7ef8e4ca0613f 100644
--- a/content/browser/devtools/devtools_external_agent_proxy_impl.cc
+++ b/content/browser/devtools/devtools_external_agent_proxy_impl.cc
@@ -5,6 +5,7 @@
 #include "content/browser/devtools/devtools_external_agent_proxy_impl.h"
 
 #include "content/browser/devtools/devtools_agent_host_impl.h"
+#include "content/browser/devtools/devtools_manager_impl.h"
 #include "content/public/browser/devtools_external_agent_proxy_delegate.h"
 
 namespace content {
@@ -59,6 +60,12 @@ scoped_refptr<DevToolsAgentHost> DevToolsExternalAgentProxyImpl::
   return agent_host_;
 }
 
+void DevToolsExternalAgentProxyImpl::DispatchOnClientHost(
+    const std::string& message) {
+  DevToolsManagerImpl::GetInstance()->DispatchOnInspectorFrontend(
+      agent_host_, message);
+}
+
 void DevToolsExternalAgentProxyImpl::ConnectionClosed() {
   agent_host_->ConnectionClosed();
 }