Fix SecurityStateTabHelperTest.DefaultSecurityLevelOn*FilesystemUrl tests with network service.

The problem was that empty filesystem objects weren't calling URLLoaderClient::OnReceiveResponse.

Bug: 769401
Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: I3e9266848642f9fa7d761b605370335441d94511
Reviewed-on: https://chromium-review.googlesource.com/1110275Reviewed-by: Chris Mumford <cmumford@chromium.org>
Commit-Queue: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569627}

content/browser/fileapi/file_system_url_loader_factory.cc

@@ -489,6 +489,11 @@ class FileSystemFileURLLoader : public FileSystemEntryURLLoader {
     int64_t bytes_to_read = std::min(
         static_cast<int64_t>(kDefaultFileSystemUrlPipeSize), remaining_bytes_);
     if (!bytes_to_read) {
+      if (consumer_handle_.is_valid()) {
+        // This was an empty file; make sure to call OnReceiveResponse
+        // regardless.
+        client_->OnReceiveResponse(head_);
+      }
       OnFileWritten(MOJO_RESULT_OK);
       return;
     }

testing/buildbot/filters/mojo.fyi.network_browser_tests.filter

@@ -13,10 +13,6 @@
 -ProcessManagerBrowserTest.NestedURLNavigationsToExtensionAllowed
 -ProxySettingsApiTest.ProxyEventsInvalidProxy
 -RegisterProtocolHandlerBrowserTest.CustomHandler
--SecurityStateTabHelperTest.DefaultSecurityLevelOnFilesystemUrl/0
--SecurityStateTabHelperTest.DefaultSecurityLevelOnFilesystemUrl/1
--SecurityStateTabHelperTest.DefaultSecurityLevelOnSecureFilesystemUrl/0
--SecurityStateTabHelperTest.DefaultSecurityLevelOnSecureFilesystemUrl/1
 -SSLUITest.TestBadHTTPSDownload/0
 -SSLUITest.TestBadHTTPSDownload/1
 -SubresourceFilterBrowserTest.FailedProvisionalLoadInMainframe