[DevTools] Implement DevToolsManager::Observer which notifies about target updates.

content/browser/devtools/render_view_devtools_agent_host.cc

Index: content/browser/devtools/render_view_devtools_agent_host.cc
diff --git a/content/browser/devtools/render_view_devtools_agent_host.cc b/content/browser/devtools/render_view_devtools_agent_host.cc
index 7045b37ab2eb82f93d1f631be7c0de8e5192f15f..75352010f016203b4935ce0b04be4250c6feec99 100644
--- a/content/browser/devtools/render_view_devtools_agent_host.cc
+++ b/content/browser/devtools/render_view_devtools_agent_host.cc
@@ -123,6 +123,7 @@ RenderViewDevToolsAgentHost::RenderViewDevToolsAgentHost(RenderViewHost* rvh)
   power_handler_->SetNotifier(notifier);
   g_instances.Get().push_back(this);
   AddRef();  // Balanced in RenderViewHostDestroyed.
+  DevToolsManager::GetInstance()->AgentHostChanged(this);
 }
 
 WebContents* RenderViewDevToolsAgentHost::GetWebContents() {
@@ -290,6 +291,7 @@ void RenderViewDevToolsAgentHost::RenderViewDeleted(RenderViewHost* rvh) {
   scoped_refptr<RenderViewDevToolsAgentHost> protect(this);
   HostClosed();
   ClearRenderViewHost();
+  DevToolsManager::GetInstance()->AgentHostChanged(this);
   Release();
 }
 
@@ -339,6 +341,16 @@ void RenderViewDevToolsAgentHost::DidDetachInterstitialPage() {
   overrides_handler_->DidDetachInterstitialPage();
 }
 
+void RenderViewDevToolsAgentHost::TitleWasSet(
+    NavigationEntry* entry, bool explicit_set) {
+  DevToolsManager::GetInstance()->AgentHostChanged(this);
+}
+
+void RenderViewDevToolsAgentHost::NavigationEntryCommitted(
+    const LoadCommittedDetails& load_details) {
+  DevToolsManager::GetInstance()->AgentHostChanged(this);
+}
+
 void RenderViewDevToolsAgentHost::Observe(int type,
                                           const NotificationSource& source,
                                           const NotificationDetails& details) {