Discovery API supports specifying a tile in a URL.

chrome/browser/ui/webui/ntp/suggestions_source_discovery.cc

Index: chrome/browser/ui/webui/ntp/suggestions_source_discovery.cc
diff --git a/chrome/browser/ui/webui/ntp/suggestions_source_discovery.cc b/chrome/browser/ui/webui/ntp/suggestions_source_discovery.cc
index 2aa595579c5a28a8051c1405af46fd94265e2d8b..4e89fbe069769b4ff174bda8e3d0cb6f2d7edc12 100644
--- a/chrome/browser/ui/webui/ntp/suggestions_source_discovery.cc
+++ b/chrome/browser/ui/webui/ntp/suggestions_source_discovery.cc
@@ -76,6 +76,9 @@ void SuggestionsSourceDiscovery::FetchItems(Profile* profile) {
                                       ASCIIToUTF16((*it)->link_text()),
                                       GURL((*it)->link_url()));
     page_value->SetDouble("score", (*it)->score());
+    const std::string& url_image = (*it)->url_image();
+    if (url_image.length() > 0)

[Evan Stade, 2012/07/26 04:26:02]

I don't think there's any need for this check.

[beaudoin, 2012/07/26 17:08:37]

It is needed because url_image is an optional parameter in the API. If it's
missing from the page_value dictionary we want to use the Chrome-provided
thumbnail. It makes it possible for an extension to suggest an item from
Chrome's history without having to provide an image for it.

+      page_value->SetString("urlImage", url_image);
     items_.push_back(page_value);
   }
   combiner_->OnItemsReady();