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

chrome/browser/devtools/chrome_devtools_manager_delegate.h

Index: chrome/browser/devtools/chrome_devtools_manager_delegate.h
diff --git a/chrome/browser/devtools/chrome_devtools_manager_delegate.h b/chrome/browser/devtools/chrome_devtools_manager_delegate.h
index 6dcaef263c9c6242ddad29abd461d8ea9d4b5ccb..af544ef8076bcf0db33719ff730747a5cc0d81ac 100644
--- a/chrome/browser/devtools/chrome_devtools_manager_delegate.h
+++ b/chrome/browser/devtools/chrome_devtools_manager_delegate.h
@@ -26,6 +26,8 @@ class ChromeDevToolsManagerDelegate :
   static char kTypeBackgroundPage[];
   static char kTypeWebView[];
 
+  static std::string GetBrowserGUID();
+
   ChromeDevToolsManagerDelegate();
   ~ChromeDevToolsManagerDelegate() override;
 
@@ -44,6 +46,7 @@ class ChromeDevToolsManagerDelegate :
       const GURL& url) override;
   std::string GetDiscoveryPageHTML() override;
   std::string GetFrontendResource(const std::string& path) override;
+  std::string GetBrowserTargetGUID() override;
 
   // content::DevToolsAgentHostObserver overrides.
   void DevToolsAgentHostAttached(