Add support for pulling icons for OfflineItems

components/offline_items_collection/core/offline_content_provider.h

Index: components/offline_items_collection/core/offline_content_provider.h
diff --git a/components/offline_items_collection/core/offline_content_provider.h b/components/offline_items_collection/core/offline_content_provider.h
index 353a7bc25205f915961660263132cc9b55fd614d..a8026f999316a3572bb987971f67f11fef967df8 100644
--- a/components/offline_items_collection/core/offline_content_provider.h
+++ b/components/offline_items_collection/core/offline_content_provider.h
@@ -8,6 +8,7 @@
 #include <string>
 #include <vector>
 
+#include "base/callback.h"
 #include "base/macros.h"
 #include "url/gurl.h"
 
@@ -15,6 +16,7 @@ namespace offline_items_collection {
 
 struct ContentId;
 struct OfflineItem;
+struct OfflineItemVisuals;
 
 // A provider of a set of OfflineItems that are meant to be exposed to the UI.
 // The provider is required to notify all observers of OnItemsAvailable when the
@@ -23,6 +25,8 @@ struct OfflineItem;
 class OfflineContentProvider {
  public:
   using OfflineItemList = std::vector<OfflineItem>;
+  using VisualsCallback =
+      base::Callback<void(const ContentId&, const OfflineItemVisuals*)>;
 
   // An observer class that should be notified of relevant changes to the
   // underlying data source.
@@ -44,6 +48,7 @@ class OfflineContentProvider {
 
     // Called when the contents of |item| have been updated and the UI should be
     // refreshed for that item.
+    // TODO(dtrainor): Make this take a list of OfflineItems.
     virtual void OnItemUpdated(const OfflineItem& item) = 0;
 
    protected:
@@ -79,6 +84,13 @@ class OfflineContentProvider {
   // Returns all OfflineItems for this particular provider.
   virtual OfflineItemList GetAllItems() = 0;
 
+  // Asks for an OfflineItemVisuals struct for an OfflineItem represented by
+  // |id| or |nullptr| if one doesn't exist.  The caller should post any

[nyquist, 2017/04/13 05:08:25]

The "caller"? Do you mean the implementor of the interface?

[David Trainor- moved to gerrit, 2017/04/13 07:20:23]

Ah yeah sorry thanks!

+  // replies even if the results are available immediately to prevent reentrancy
+  // and for consistent behavior.
+  virtual void GetVisualsForItem(const ContentId& id,
+                                 const VisualsCallback& callback) = 0;
+
   // Adds an observer that should be notified of OfflineItem list modifications.
   // If the provider is already initialized OnItemsAvailable should be scheduled
   // on this observer (suggested over calling the method directly to avoid