[Extensions] Clean up the handling of ExtensionHostMsg_Request

extensions/shell/browser/shell_app_delegate.cc

Index: extensions/shell/browser/shell_app_delegate.cc
diff --git a/extensions/shell/browser/shell_app_delegate.cc b/extensions/shell/browser/shell_app_delegate.cc
index 38710278d8f926cee33274eb7bb815cfddebdcf8..6404964c6da1c1499d5488e3d09f5f6c5ca58461 100644
--- a/extensions/shell/browser/shell_app_delegate.cc
+++ b/extensions/shell/browser/shell_app_delegate.cc
@@ -7,6 +7,7 @@
 #include "content/public/browser/web_contents.h"
 #include "extensions/common/constants.h"
 #include "extensions/shell/browser/media_capture_util.h"
+#include "extensions/shell/browser/shell_extension_web_contents_observer.h"
 
 namespace extensions {
 
@@ -17,6 +18,7 @@ ShellAppDelegate::~ShellAppDelegate() {
 }
 
 void ShellAppDelegate::InitWebContents(content::WebContents* web_contents) {
+  ShellExtensionWebContentsObserver::CreateForWebContents(web_contents);
 }
 
 void ShellAppDelegate::RenderViewCreated(