drive: Fix computation for showing the number of fetched files

chrome/browser/chromeos/drive/gdata_wapi_feed_loader.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/drive/gdata_wapi_feed_loader.h"
 
 #include <set>
 
 #include "base/command_line.h"
 #include "base/file_util.h"
@@ skipping 725 matching lines @@
 void GDataWapiFeedLoader::OnNotifyDocumentFeedFetched(
     base::WeakPtr<GetDocumentsUiState> ui_state) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   if (!ui_state) {
     // The ui state instance is already released, which means the fetching
     // is done and we don't need to update any more.
     return;
   }
 
-  base::TimeDelta elapsed_time =
+  base::TimeDelta ui_elapsed_time =
       base::TimeTicks::Now() - ui_state->start_time;
 
   if (ui_state->num_showing_documents + kFetchUiUpdateStep <=
       ui_state->num_fetched_documents) {
     ui_state->num_showing_documents += kFetchUiUpdateStep;
     FOR_EACH_OBSERVER(GDataWapiFeedLoaderObserver, observers_,
                       OnDocumentFeedFetched(ui_state->num_showing_documents));
 
     int num_remaining_ui_updates =
         (ui_state->num_fetched_documents - ui_state->num_showing_documents)
         / kFetchUiUpdateStep;
     if (num_remaining_ui_updates > 0) {
       // Heuristically, we use fetched time duration to calculate the next
       // UI update timing.
       base::TimeDelta remaining_duration =
-          ui_state->feed_fetching_elapsed_time - elapsed_time;
+          ui_state->feed_fetching_elapsed_time - ui_elapsed_time;
+      base::TimeDelta interval = remaining_duration / num_remaining_ui_updates;
+      // If UI update is slow for some reason, the interval can be
+      // negative, or very small. This rarely happens but should be handled.
+      const int kMinIntervalMs = 10;
+      if (interval.InMilliseconds() < kMinIntervalMs)
+        interval = base::TimeDelta::FromMilliseconds(kMinIntervalMs);
+
       base::MessageLoopProxy::current()->PostDelayedTask(
           FROM_HERE,
           base::Bind(&GDataWapiFeedLoader::OnNotifyDocumentFeedFetched,
                      weak_ptr_factory_.GetWeakPtr(),
                      ui_state->weak_ptr_factory.GetWeakPtr()),
-          remaining_duration / num_remaining_ui_updates);
+          interval);
     }
   }
 }
 
 void GDataWapiFeedLoader::LoadFromCache(
     bool should_load_from_server,
     const FileOperationCallback& callback) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   LoadRootFeedParams* params = new LoadRootFeedParams(should_load_from_server,
@@ skipping 133 matching lines @@
         dir_iter != changed_dirs.end(); ++dir_iter) {
       FOR_EACH_OBSERVER(GDataWapiFeedLoaderObserver, observers_,
                         OnDirectoryChanged(*dir_iter));
     }
   }
 
   return error;
 }
 
 }  // namespace drive