Change AboutResourceLoader::GetAboutResource to wait for inflight update task.

chrome/browser/chromeos/drive/change_list_loader.cc

Index: chrome/browser/chromeos/drive/change_list_loader.cc
diff --git a/chrome/browser/chromeos/drive/change_list_loader.cc b/chrome/browser/chromeos/drive/change_list_loader.cc
index 6c46f7f439f9280cc4c4c3d8ca6f0dc3f6cc0add..5ecd19e7db2b19f00ecce0bced2c017fa7d733a6 100644
--- a/chrome/browser/chromeos/drive/change_list_loader.cc
+++ b/chrome/browser/chromeos/drive/change_list_loader.cc
@@ -209,6 +209,7 @@ void LoaderController::Unlock() {
 
 AboutResourceLoader::AboutResourceLoader(JobScheduler* scheduler)
     : scheduler_(scheduler),
+      current_update_task_id_(-1),
       weak_ptr_factory_(this) {
 }
 
@@ -219,6 +220,12 @@ void AboutResourceLoader::GetAboutResource(
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DCHECK(!callback.is_null());
 
+  // If the latest UpdateAboutResource task is still running. Wait for it,
+  if (pending_callbacks_.count(current_update_task_id_)) {
+    pending_callbacks_[current_update_task_id_].push_back(callback);
+    return;
+  }
+
   if (cached_about_resource_) {
     base::MessageLoopProxy::current()->PostTask(
         FROM_HERE,
@@ -237,34 +244,47 @@ void AboutResourceLoader::UpdateAboutResource(
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DCHECK(!callback.is_null());
 
+  ++current_update_task_id_;
+  pending_callbacks_[current_update_task_id_].push_back(callback);
+
   scheduler_->GetAboutResource(
       base::Bind(&AboutResourceLoader::UpdateAboutResourceAfterGetAbout,
                  weak_ptr_factory_.GetWeakPtr(),
-                 callback));
+                 current_update_task_id_));
 }
 
 void AboutResourceLoader::UpdateAboutResourceAfterGetAbout(
-    const google_apis::AboutResourceCallback& callback,
+    int task_id,
     google_apis::GDataErrorCode status,
     scoped_ptr<google_apis::AboutResource> about_resource) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  DCHECK(!callback.is_null());
   FileError error = GDataToFileError(status);
 
-  if (error == FILE_ERROR_OK) {
-    if (cached_about_resource_ &&
-        cached_about_resource_->largest_change_id() >
-        about_resource->largest_change_id()) {
-      LOG(WARNING) << "Local cached about resource is fresher than server, "
-                   << "local = " << cached_about_resource_->largest_change_id()
-                   << ", server = " << about_resource->largest_change_id();
-    }
+  const std::vector<google_apis::AboutResourceCallback> callbacks =
+      pending_callbacks_[task_id];
+  pending_callbacks_.erase(task_id);
 
-    cached_about_resource_.reset(
-        new google_apis::AboutResource(*about_resource));
+  if (error != FILE_ERROR_OK) {
+    for (size_t i = 0; i < callbacks.size(); ++i)
+      callbacks[i].Run(status, scoped_ptr<google_apis::AboutResource>());
+    return;
   }
 
-  callback.Run(status, about_resource.Pass());
+  // Updates the cache when the resource is successfully obtained.
+  if (cached_about_resource_ &&
+      cached_about_resource_->largest_change_id() >
+      about_resource->largest_change_id()) {
+    LOG(WARNING) << "Local cached about resource is fresher than server, "
+                 << "local = " << cached_about_resource_->largest_change_id()
+                 << ", server = " << about_resource->largest_change_id();
+  }
+  cached_about_resource_.reset(new google_apis::AboutResource(*about_resource));
+
+  for (size_t i = 0; i < callbacks.size(); ++i) {
+    callbacks[i].Run(
+        status,
+        make_scoped_ptr(new google_apis::AboutResource(*about_resource)));
+  }
 }
 
 ChangeListLoader::ChangeListLoader(