recent: Fix crash in OnGetRecentFiles()

render_frame_host() can be null after finishing async operations.
Remove DCHECK to stop accessing it.

BUG=762797
TEST=build
[email protected]

(cherry picked from commit 9ccbde3)

Change-Id: I2e05eca525bea28fb1ac3d75f3dbc500c7bd50c7
Reviewed-on: https://chromium-review.googlesource.com/654279
Reviewed-by: Tomasz Mikolajewski <[email protected]>
Reviewed-by: Shuhei Takahashi <[email protected]>
Commit-Queue: Ryo Hashimoto <[email protected]>
Cr-Original-Commit-Position: refs/heads/master@{#500229}
Reviewed-on: https://chromium-review.googlesource.com/656745
Reviewed-by: Ryo Hashimoto <[email protected]>
Cr-Commit-Position: refs/branch-heads/3202@{#84}
Cr-Branched-From: fa6a5d8-refs/heads/master@{#499098}

chrome/browser/chromeos/extensions/file_manager/private_api_misc.cc

@@ -750,19 +750,8 @@ FileManagerPrivateInternalGetRecentFilesFunction::Run() {
 void FileManagerPrivateInternalGetRecentFilesFunction::OnGetRecentFiles(
     api::file_manager_private::SourceRestriction restriction,
     const std::vector<chromeos::RecentFile>& files) {
-  scoped_refptr<storage::FileSystemContext> file_system_context =
-      file_manager::util::GetFileSystemContextForRenderFrameHost(
-          chrome_details_.GetProfile(), render_frame_host());
-  DCHECK(file_system_context.get());
-
-  const storage::ExternalFileSystemBackend* external_backend =
-      file_system_context->external_backend();
-  DCHECK(external_backend);
-
   file_manager::util::FileDefinitionList file_definition_list;
   for (const auto& file : files) {
-    DCHECK(external_backend->CanHandleType(file.url().type()));
-
     // Filter out files from non-allowed sources.
     // We do this filtering here rather than in RecentModel so that the set of
     // files returned with some restriction is a subset of what would be