Add support for providing an external file for extracting content.

components/dom_distiller/content/distiller_page_web_contents.h

Index: components/dom_distiller/content/distiller_page_web_contents.h
diff --git a/components/dom_distiller/content/distiller_page_web_contents.h b/components/dom_distiller/content/distiller_page_web_contents.h
index e73b0ccc9b04e5780664768f3189e76507e171b6..ac825ac51d9ca87d608aa373e661cc37dd708477 100644
--- a/components/dom_distiller/content/distiller_page_web_contents.h
+++ b/components/dom_distiller/content/distiller_page_web_contents.h
@@ -34,6 +34,8 @@ class DistillerPageWebContentsFactory : public DistillerPageFactory {
   explicit DistillerPageWebContentsFactory(
       content::BrowserContext* browser_context)
       : DistillerPageFactory(), browser_context_(browser_context) {}
+  DistillerPageWebContentsFactory(content::BrowserContext* browser_context,
+                                  std::string distiller_js_script);
   ~DistillerPageWebContentsFactory() override {}
 
   scoped_ptr<DistillerPage> CreateDistillerPage(
@@ -43,6 +45,8 @@ class DistillerPageWebContentsFactory : public DistillerPageFactory {
 
  private:
   content::BrowserContext* browser_context_;
+  // An optional script for overriding the JS that comes packaged with Chrome.
+  std::string distiller_js_script_;
 };
 
 class DistillerPageWebContents : public DistillerPage,