Avoid crashes when loading chrome://drive-internals with DriveFS.

With DriveFS, a number of DriveIntegrationService fields are nullptr
because they are no longer used by DriveFS.

BUG=845393

Change-Id: Ibafa2d02264059d3383c91c491ee770deb6e4632
Reviewed-on: https://chromium-review.googlesource.com/1116202
Commit-Queue: Anand Mistry <amistry@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571020}

chrome/browser/ui/webui/chromeos/drive_internals_ui.cc

@@ -434,24 +434,31 @@ void DriveInternalsWebUIHandler::OnPageLoaded(const base::ListValue* args) {
   if (!integration_service)
     return;
 
+  UpdateDriveRelatedPreferencesSection();
+  UpdateGCacheContentsSection();
+  UpdateLocalStorageUsageSection();
+  UpdatePathConfigurationsSection();
+
   drive::DriveServiceInterface* drive_service =
       integration_service->drive_service();
-  DCHECK(drive_service);
-  drive::DebugInfoCollector* debug_info_collector =
-      integration_service->debug_info_collector();
-  DCHECK(debug_info_collector);
-
-  UpdateDriveRelatedPreferencesSection();
+  if (drive_service) {
     UpdateConnectionStatusSection(drive_service);
     UpdateAboutResourceSection(drive_service);
     UpdateAppListSection(drive_service);
+  }
+
+  drive::DebugInfoCollector* debug_info_collector =
+      integration_service->debug_info_collector();
+  if (debug_info_collector) {
     UpdateLocalMetadataSection(debug_info_collector);
     UpdateDeltaUpdateStatusSection(debug_info_collector);
-  UpdateInFlightOperationsSection(integration_service->job_list());
-  UpdateGCacheContentsSection();
     UpdateCacheContentsSection(debug_info_collector);
-  UpdateLocalStorageUsageSection();
-  UpdatePathConfigurationsSection();
+  }
+
+  drive::JobListInterface* job_list = integration_service->job_list();
+  if (job_list) {
+    UpdateInFlightOperationsSection(job_list);
+  }
 
   // When the drive-internals page is reloaded by the reload key, the page
   // content is recreated, but this WebUI object is not (instead, OnPageLoaded
@@ -887,8 +894,12 @@ void DriveInternalsWebUIHandler::OnPeriodicUpdate(const base::ListValue* args) {
   if (!integration_service)
     return;
 
-  UpdateInFlightOperationsSection(integration_service->job_list());
   UpdateEventLogSection();
+
+  drive::JobListInterface* job_list = integration_service->job_list();
+  if (job_list) {
+    UpdateInFlightOperationsSection(job_list);
+  }
 }
 
 }  // namespace