Introduce NetworkDelegate's implementation in extensions.

extensions/common/switches.cc

Index: extensions/common/switches.cc
diff --git a/extensions/common/switches.cc b/extensions/common/switches.cc
index 362630bdf057488efd8d729a345b38c8613ee46a..2477d53b9372d374c15d9b1a61f893de7dc5e553 100644
--- a/extensions/common/switches.cc
+++ b/extensions/common/switches.cc
@@ -19,6 +19,9 @@ const char kAllowLegacyExtensionManifests[] =
 // Enables the <appview> tag in platform apps.
 const char kAppView[] = "app-view";
 
+// Request pages to be dumped as text once they finished loading.
+const char kDumpRenderTree[] = "dump-render-tree";
+
 // Enables extension options to be embedded in chrome://extensions rather than
 // a new tab.
 const char kEmbeddedExtensionOptions[] = "embedded-extension-options";