Provide API in RequestCoordinator to remove results by client ID.

components/offline_pages/background/request_coordinator.h

Index: components/offline_pages/background/request_coordinator.h
diff --git a/components/offline_pages/background/request_coordinator.h b/components/offline_pages/background/request_coordinator.h
index c757702b01bace4e290c725600225bb70b7e3e28..2588345c8e773f3c2ac63c3370216e310e38f080 100644
--- a/components/offline_pages/background/request_coordinator.h
+++ b/components/offline_pages/background/request_coordinator.h
@@ -50,6 +50,10 @@ class RequestCoordinator : public KeyedService {
   bool SavePageLater(
       const GURL& url, const ClientId& client_id, bool user_reqeusted);
 
+  // Cancel a list of requests by |client_id|.  This removes requests from the
+  // request queue, but does not cancel an in-progress pre-render.

[dougarnett, 2016/07/29 19:01:23]

interesting question about how to deal with a pending request. Canceling would
be clear but if we don't, what happens when request completes and does not find
its original request?

[I think I favor this just being a queue operation and graceful handling of
missing request]

[Pete Williamson, 2016/07/29 22:48:52]

Per offline discussion, let's leave this as is, and later add code to cancel the
pending request.  TODO added.

+  void CancelRequests(const std::vector<ClientId>& client_ids);

[dougarnett, 2016/07/29 19:01:24]

RemoveRequests more accurate since removed requests could already be complete?  

[Pete Williamson, 2016/07/29 22:48:52]

Done.

+
   // Starts processing of one or more queued save page later requests.
   // Returns whether processing was started and that caller should expect
   // a callback. If processing was already active, returns false.