[Offline Pages] Adds UMA for result of attempts to immediately start background loading.

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 537e5a85df475cd6b747f28e5facdab6ca6170a1..64e13cd256bc1f9f00ef1657f95d6dd6a179ce49 100644
--- a/components/offline_pages/background/request_coordinator.h
+++ b/components/offline_pages/background/request_coordinator.h
@@ -169,6 +169,26 @@ class RequestCoordinator : public KeyedService,
   }
 
  private:
+  // Immediate start attempt status code for UMA.
+  // For any changes, also update corresponding histogram in histograms.xml.
+  enum OfflinerImmediateStartStatus {
+    // Did start processing request.
+    STARTED = 0,
+    // Already busy processing a request.
+    BUSY = 1,
+    // The Offliner did not accept processing the request.
+    NOT_ACCEPTED = 2,
+    // No current network connection.
+    NO_CONNECTION = 3,
+    // Weak network connection (worse than 2G speed)
+    // according to network quality estimator.
+    WEAK_CONNECTION = 4,
+    // Did not start because this is svelte device.
+    NOT_STARTED_ON_SVELTE = 5,
+    // NOTE: insert new values above this line and update histogram enum too.
+    STATUS_COUNT = 6,
+  };
+
   // Receives the results of a get from the request queue, and turns that into
   // SavePageRequest objects for the caller of GetQueuedRequests.
   void GetQueuedRequestsCallback(
@@ -205,6 +225,8 @@ class RequestCoordinator : public KeyedService,
   // as to other device conditions).
   void StartProcessingIfConnected();
 
+  OfflinerImmediateStartStatus TryImmediateStart();
+
   // Check the request queue, and schedule a task corresponding
   // to the least restrictive type of request in the queue.
   void ScheduleAsNeeded();