DevTools: enable target domain handler on the browser target, make browser target non-discoverable.

content/public/browser/devtools_manager_delegate.cc

Index: content/public/browser/devtools_manager_delegate.cc
diff --git a/content/public/browser/devtools_manager_delegate.cc b/content/public/browser/devtools_manager_delegate.cc
index b4d12ed947a1b8851baba0c75c5accdf20e1586e..9713b26617b1480d55d90404c8f517f4951b568b 100644
--- a/content/public/browser/devtools_manager_delegate.cc
+++ b/content/public/browser/devtools_manager_delegate.cc
@@ -48,6 +48,11 @@ std::string DevToolsManagerDelegate::GetFrontendResource(
   return std::string();
 }
 
+// Returns browser endpoint for remote debugging.
+std::string DevToolsManagerDelegate::GetBrowserTargetGUID() {
+  return std::string();
+}
+
 DevToolsManagerDelegate::~DevToolsManagerDelegate() {
 }