Improve syncing between dom distiller and the print preview request

components/dom_distiller/core/dom_distiller_service.h

Index: components/dom_distiller/core/dom_distiller_service.h
diff --git a/components/dom_distiller/core/dom_distiller_service.h b/components/dom_distiller/core/dom_distiller_service.h
index 5d2558d1142b68467f6434f8b538663a16cd7762..7e614c36693e6ca694a4bac2706d79de368f4da8 100644
--- a/components/dom_distiller/core/dom_distiller_service.h
+++ b/components/dom_distiller/core/dom_distiller_service.h
@@ -92,6 +92,10 @@ class DomDistillerServiceInterface {
       scoped_ptr<DistillerPage> distiller_page,
       const GURL& url) = 0;
 
+  virtual scoped_ptr<ViewerHandle> AddViewRequestDelegate(

[nyquist, 2016/01/20 16:59:08]

Please add an explanatory comment as to how this is supposed to be used, and the
expected return values.

What happens if there was no request to distill the URL from before? Does that
do anything? If the distillation has already started, will all callbacks arrive?
If distillation has just finished, what will this return, and what types of
callbacks can you assume?

[mvendramini_hp, 2016/01/21 16:54:46]

Noted. I suggest we keep this pending until we solve the first comment (whether
to use GetOrCreateTaskTrackerForUrl or GetTaskTrackerForUrl, for instance) - as
soon as we agree on that one, we'll add documentation to this new operation.

+      ViewRequestDelegate* delegate,
+      const GURL& url) = 0;
+
   // Creates a default DistillerPage.
   virtual scoped_ptr<DistillerPage> CreateDefaultDistillerPage(
       const gfx::Size& render_view_size) = 0;
@@ -137,6 +141,8 @@ class DomDistillerService : public DomDistillerServiceInterface {
   scoped_ptr<ViewerHandle> ViewUrl(ViewRequestDelegate* delegate,
                                    scoped_ptr<DistillerPage> distiller_page,
                                    const GURL& url) override;
+  scoped_ptr<ViewerHandle> AddViewRequestDelegate(ViewRequestDelegate* delegate,
+                                                  const GURL& url) override;
   scoped_ptr<DistillerPage> CreateDefaultDistillerPage(
       const gfx::Size& render_view_size) override;
   scoped_ptr<DistillerPage> CreateDefaultDistillerPageWithHandle(