DevTools: Add parent id to target descriptor in remote debugging.

content/shell/browser/shell_devtools_delegate.cc

Index: content/shell/browser/shell_devtools_delegate.cc
diff --git a/content/shell/browser/shell_devtools_delegate.cc b/content/shell/browser/shell_devtools_delegate.cc
index d6f3b626476d1b7ea94a1cfedea996f16529ba34..6a8f09e047e1a16fa534c9a3fe3570763f174f2b 100644
--- a/content/shell/browser/shell_devtools_delegate.cc
+++ b/content/shell/browser/shell_devtools_delegate.cc
@@ -77,6 +77,7 @@ class Target : public content::DevToolsTarget {
   explicit Target(WebContents* web_contents);
 
   virtual std::string GetId() const OVERRIDE { return id_; }
+  virtual std::string GetParentId() const OVERRIDE { return std::string(); }
   virtual std::string GetType() const OVERRIDE { return kTargetTypePage; }
   virtual std::string GetTitle() const OVERRIDE { return title_; }
   virtual std::string GetDescription() const OVERRIDE { return std::string(); }